Do you have the reference to this? I read it somewhere, but I can’t find it any more. Moreover, I thought he was referring to the 2Qute, and said the USB implementation in the Qutest was best.
I think optical is his preferred choice from what I have read.
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That was my understanding, too, for my Qutest, which I use with an Allo DigiONE, but I’m sure Watt’s said that USB was equal in the newer DACs. But, I can’t find anything on this now … not that it matters as I’m unlikely to upgrade.
Read it on the Qutest Head-Fi thread, I am sure. It was a long comment by Rob Watts on FPGA and USB … I will search for it.
But that can take a while, because I’m struggling with setting up the Christmas tree. Defending it as best I can against the cat, who mistakes it for the cherry tree on whose trunk he always runs up 
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@CrystalGipsy
I think you’re right about that.
I’ve searched…there was a link on Head-Fi to an 2019 interview with Rob Watts about Qutest with a detailed review of the sources.
But that doesn’t seem to be available anymore?
Anyway, my bad! Sorry
Thanks for posting. I think this is where I read about this, too, which may explain why I couldn’t find it again.
I am reading the thread, and found a few snippets from Rob regarding isolation (on the Qutest, which is much better than with my 2Qute) that debunks the use of USB “decrapifiers”. He goes on to explain that these can reintroduce ground loops and bypass any galvanic isolation in the DAC.
Additionally, there is a discussion about the SMPS and why this (or a battery) should be used with the Qutest for best performance, and elsewhere, on the faults of audiophile USB and BNC cables. But nothing regarding preference for BNC over USB.
I’m going to stop reading now, to avoid risking FOMO setting in. 
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Hi Martin
I have a Qutest and have gone a little way down the rabbit hole on USB vs SPDIF. An important consideration for me is my preference for HQPlayer and upsampling to the maximum PCM rate of the Qutest 705k/768k. Using USB I was often the victim of brain frying white noise on occasion, normally when the base rate switched from 44.1k to 48k family.
I noticed some discussions about a device that converts USB to dual BNC (SPDIF) namely the SRC-DX. The thread below on AS is one such and folks on there way more knowledgable than me claim that using the dual BNC bypasses the Qutest’s Amanero USB chip, allows 705/768k and perhaps offers an improved sound.
I have the SRC-DX in my set up and yes I think it probably sounds a bit smoother (though not sure I would pass a blind test), but it definitely avoids the white noise issue on USB and illuminates the Qutest source light in a lovely turquoise (dual bnc).
Also interesting to note that the M-Scalar outputs using dual BNC rather than USB, presumably there is a reason for that?
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Well, my reason for using S/PDIF was the pops and clicks I had on USB. They’re not present now, and I suspect my original Raspberry Pi was the older 2B variant. I’ve never experienced white noise when switching; you may find Roon can help with this using Rsync Delay.
The dual BNC is needed for bandwidth since S/PDIF is limited to 192 kHz 24 bit, whereas dual BNC takes this up to 768 kHz.
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I went on trying S/PDIF vs USB again during the holidays from Auralic Aries G2 to Chord m-scaler (followed by dual BNC to DAVE). If there was any auditable difference I preferred USB. Saying “if” since I think any difference might be due to trying to distinguish differences in the first place.
Also ran the m-scaler of battery (Ecoflow R600), but without finding any conclusive evidence that this was something I (or my friends) preferred.
My guess here is that if the source is “noisy” then the optical might be preferable. And if your electrical grid is then possibly battery makes a difference. I live quite rural so not that many neighbors and no heavy electricity usage anywhere near where I live. Possibly a lot of DC in the grid from domestic appliances. Still I couldn’t distinguish any difference between the grid and battery during that hour of testing a couple of days ago.
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