I know, I can either use toslink directly from computer, or USB through an ethernet transport like opticalRendu. My question is if an ethernet transport would give some additional SQ compared to toslink, if the DAC handles toslink well.
It really depends on the design of the USB to TOSLink device.
My explanation skills seems lacking! I mean toslink directly from computer, no converter.
If we keep things concrete, which of these two would sound best:
- Computer -> toslink -> Chord Qutest
- Computer -> ethernet switch -> fiber -> opticalRendu -> Chord Qutest
If this is bit perfect (should be from computer hopefully, with the right exclusive mode settings) then you have absolute perfect input isolation.
Sample rate support is obviously limited with TOSlink but may not be an issue for you - depending on your collection.
Jitter can be an issue with TOSlink with some DACs… and I won’t say it’s a non-issue but it’s probably the least of your issues with the Qutest…
It’s no surprise Rob Watts says the TOSlink input is the one to beat with his DACs (assuming bit perfect playback and sample rate limitation is not an issue for the user).
You’ll need to get the opticalRendu (when it’s out…) and do the comparison for us 
Those measurements would likely have been done with the low jitter output of the AP.
Anyway, I would not waste my time with TOSlink because of the limitations already discussed and instead I would use USB.
The customer needs to decide if they want a regular computer in audio room or a small endpoint like a Rendu. Personally, I have not had a regular computer in my audio room in ages.
True but Rob says the measurements are identical with up to 2us of input jitter… with lots of measurements of his gear at the limit of even the APx555 machine, at some point ya gotta believe him…
Some people are fine with up to PCM24/96… so TOSlink wouldn’t be an issue for them. Depends on the person. Some TOSlink sources I have are even fine with up to PCM24/192kHz… DoP64 is a great test of bit perfect playback and these sources pass…
Some of us have a computer at the office/desk and often listen there… quite normal 
Anyway, I hope @Magnus orders an opticalRendu so he can answer all these questions he has and share with us.
I’ll probably be getting one at some point too.
I didn’t say I distrust him. Agree some people are fine with 24/96, but the feedback I get is that most are not. While some devices support TOSlink at higher rates its not typical or usual. For local playback I have no issue with local streaming.
The reasons I ask is that I am planning to upgrade both my DAC and power-amp, and if I need to factor in an opticalRendu I have to decrease the cost of the other components. For example, for around $3000 I could get a Chord Qutest and a Nord One amplifier (Ncore NC500 based). If I also need to factor in an opticalRendu, I have to select less expensive DAC and amp (the reason I probably will chose a class-D amp is because I can’t fit some big class A/AB power amps).
I currently have a DSD512/PCM768 capable system, but I pretty much only listen to PCM at 192 anyway, and sometimes I even prefer no upsampling at all. And I let Roon handle the first unfold for MQA. So if SQ is same with toslink and a good ethernet transport, I would select toslink and put the money on better DAC and power amp instead.
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I work from home (IT consultant) and listen to music in my work place. My “office” looks a lot more like a studio than an office though 
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And only use digital (software) volume control?
Be careful with this… it can be fine… can also be disastrous…
Hugo2 might be better/safer, with it’s variable output and remote control included… so it’s better suited as a preamp into a power amp.
Even your ProJect S2 can be used as a pre, with it’s included remote control.
Agreed, I think opticalRendu will be an awesome ethernet transport, and in a typical living room HiFi setup I would probably use it as a Roon endpoint.
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I’m using a Rendu at my desk setup right now.
But I use HQPlayer (up to PCM768kHz and DSD512 sample rates) so TOSlink is not an option, only for that reason.
I like the network isolation of the Rendu, even at my desk. Much better than direct USB connection (to my ears).
But then jitter wouldn’t be the thing you were “correcting” with a transport such as opticalRendu. I’m using the Chord DAVE and noticed a quite significant difference when I switched from ultraRendu with UpTone LPS-1 to Auralic Aries G2. And the funny thing is that I didn’t expect there to be any.
I currently do WiFi to my Aries G2 so I don’t know if optical would do any difference. But I love that things evolve and I missed this kind of product when I was “out shopping” last time. 
Yes, he’s not suggesting to correct anything.
Further up we were talking about TOSlink, where jitter can sometimes be a problem on some DAC’s TOSlink input.
But with Qutest, RME ADI-2, jitter on the TOSlink input is (objectively) the least of the issues to be concerned about… as long as the sample rate limitation is not an issue (depends on the person, varies) TOSlink provides perfect isolation and jitter is a non-issue with these DACs specifically.
Rob Watts will happily tell you that Dave’s USB input isolation is not perfect… there is still coupling capacitance. So there is a mechanism for different USB sources to potentially sound different, even with Dave… Your observation doesn’t surprise me at all and I observed the same when I had Dave…
TOSlink, on the other hand, provides perfect isolation from mains RF / groundloops / leakage current loops. This is why Rob himself will tell you TOSlink is the input to beat with his DACs… incoming jitter is not a concern with his DACs…
On the Dave thread on Head-Fi:
He’s talking from the technical perspective (as the designer…). If someone prefers other inputs and other sources, it’s possible they are preferring slightly increased RF / noise.
Nothing at all wrong with that of course but if the designer says the TOSlink input is technically the best, it’s probably correct for that particular DAC.
If someone thinks Rob has it wrong with Dave, don’t argue with me - go and tell him over on Head-Fi 
I think he has also said that all USB sounds the same.
Anyway, you said that, “If someone prefers other inputs and other sources, it’s possible they are preferring slightly increased RF / noise.” You don’t know that for sure though and it can just be that the source is as good or better compared to optical.
Another thing to consider is the design of some optical outputs on motherboards. Not all of them support both 44.1x and 48x rates. Some support just 48x rates which requires unwanted re-sampling. Some also utilize an inexpensive oscillator that is between the proper frequency needed to produce 44.1x and 48x rates. This means that your output is crap before it ever gets to your DAC. BTW I’m not against people using TOSlink as long as they understand it’s limitations.
He’s said what I mentioned above that Dave’s USB isolation is not perfect. Even a $50 jitterbug made a difference with Dave’s USB input to his ears… here is the proof (his words not mine or yours):
https://www.head-fi.org/threads/chord-electronics-dave.766517/page-230#post-12681548
That’s why I carefully selected my words “it’s possible”. This inherently means, maybe not… but see Rob Watt’s post above talking about RF anyway.
Simple test, which I mentioned further up, is DoP64… this will confirm if any re-sampling is happening. Assuming the source and TOSlink cable and DAC input are capable of DoP64/PCM176 rates of course… not all are of course but I’ve had many TOSlink sources that can (Bluesound Node 2, Oppo players, miniDSP USBStreamer…).
I was being sarcastic…it’s a long story. Yes, you were being careful, but not balanced IMO in the way you presented it with a negative conclusion attached to your “possible” disclaimer. If there are two possible outcomes then you should state both and not show bias towards one. The issue I wrote about deals with inherent jitter of the signal based on the lack of proper source clocking on some gear. Re-sampling is a separate issue or a concurrent issue on some gear. Yes, some gear is better than others in this respect as expected.
Anyway, as interesting is TOSlink is or isn’t…it’s off top in this thread. I would like to continue the discussion of the opticalRendu and opticalModule.
Ahh but the background comes from the designer of the DAC we are talking about… not my personal opinion/bias… check the link I posted If you want to argue if RF is not the cause why different sources can sound different with Dave, take it up with the designer of Dave himself over on Head-Fi, not me … 
That will be a fun argument to watch though.
I already requested further up, out of courtesy and respect to you, that mods move the off-topic posts. So when they see these messages, these will be moved somewhere else. @andybob