I tried native DSD over toslink but could not get it working, so my guess is DSD over DoP (DoP or native does not matter for SQ though, although DoP takes a little extra bandwidth).
The direct-DSD function in the RME DAC is to make the DAC handle DSD directly (which means disable volume and DSP). That means full volume, so don’t try it if using RME as preamp. The normal DSD handling is like in Roon, i.e. it converts to PCM before volume and DSP is applied.
Some comparisons with Hugo 2 here, which I think you are familiar with: https://headfonics.com/2018/04/rme-adi-2-dac-review/
You are potentially comparing different preamp design and digital volume controls . The ADI-2 DAC can be better optimized as a pre, with different gain settings… The Pro-Ject S2 DAC can’t.
But in your case (straight into power amps) it’s definitely a good feature to have.
I’m not a fan of the S2 DAC’s digital volume control, especially when you get down low. But now I use it as a straight D-to-A converter only, fixed at 0dB volume…
From what I read and experienced myself, the implementation of digital volume in RME is excellent, especially in combination with auto-ref which sets the ref-voltage based on volume and sensitivity of amplifier automatically to maximize dynamic range.
Another excellent feature: I often listen when wife is sleeping, so have to listen at low volume. And I absolutely love the configurable loudness function, toggling it on/off at low volume is like going from music over a telephone line to real music.
Here is how it works:
So now when I play at -57dB I get +8dB bass and +5dB treble, and that lowers gradually as I raise volume to -37dB at which point its 0/0. No reason to ever fiddle with it, I leave it on at all time and let it do its magic.
Surprising that not more DAC has this feature, its a total game changer for listening at low volume. But it does require a good display and proper build in DPS, so maybe not so strange.
Yeh I’ve had an extensive home demo myself… as a straight DAC (no digital vol. control) and short unbalanced RCA cables to amp, the difference wasn’t so big with the Pro-Ject S2 DAC I have (subjectively, to my ears/tastes).
It’s built-in headphone amp section does subjectively perform better to my ears/tastes than the S2 DAC’s built-in amp, but I use a separate headphone amp anyway (THX 789 amp) so I don’t really care about that particular difference.
The preamp features are much better with the RME. Very useful when connecting to power amps or powered speakers… I may get it as a DAC+pre direct into powered speakers… just waiting on news on a couple upcoming products first, before deciding.
The other very obvious different with the RME is the option to go balanced XLR on outputs… can be a big advantage, depending on overall system and layout.
Got it working now, bought a cheap toslink sound card Delock 7.1 which support everything up to 192khz, and also have both WASAPI and ASIO. I don’t think the sound quality changed (maybe a little added clarity), but playing DSD DoP over toslink to RME now works excellent (RME reports “sync 176,4 DSD 24” on state overview).
A new review: https://www.themasterswitch.com/review-rme-adi-2-dac
The like it better than Hugo 2 and Brooklyn+ (and it costs less than half of those)
How do you think the RME and Sennheiser HD800s will match?
I don’t use headphones, but check here its a headphone site: https://www.head-fi.org/threads/rme-adi-2-dac-thread.868015/ (lots of reading).
According to one of the RME designers (and co-founder, Matthias Carstens):
"The ADI-2 Pro easily drives HD800, 800S and the new 820 (tested last week) until your ears bleed and the driver’s cones start crackling. I would expect the specs to suffer if you put an external headamp in the loop, so let’s hear what you find out."
https://www.forum.rme-audio.de/viewtopic.php?pid=132710#p132710
I think ADI-2 DAC has the same headphone amp design and output specs as ADI-2 Pro…
I can add to that test that the earlier problems with switching sample rates has been fixed. And unlike some DACs, it switches between sample rates lightning fast and without any clicks.
About to pull the trigger for a used rme & hd800s combo for €1650. A bargain, don’t you think?
Which model exactly? Make sure it has “FS” on the front of the unit…
I think so. The pic is a bit blurry but there are 2 characters after ADI-2 DAC. Need to confirm. Why?
If it’s ADI-2 DAC you should be fine as these all have “FS” on the front. Check Google Images.
If it’s ADI-2 Pro, there was an “FS” model released later which some people have shown measures a tiny little bit better than non-FS model… So I saw some very cheap ADI-2 Pro (non-FS) up for sale in recent months.
@jaguone if you have trouble falling asleep here’s some of the background reading info 
http://www.rme-audio.de/en/support/techinfo/steadyclock.php
"Today (2018) SteadyClock is still the same, with a few small improvements in the latest FS version, like even more efficient filtering, and a design based on a super low jitter reference clock. Something that changed over time is the clock rate of the DDS (Direct Digital Synthesizer, realized within the FPGA), which runs at 800 MHz in most units, in some units even at 1 GHz. "
This should help you get to sleep much much faster 
No espresso for me after 4pm… I know it but had a shot anyway. Had a quick glance on the tech info. You’re right, I feel tired already.
Read on their forum that a new firmware will be available within a couple of weeks, which will contain some “exciting” news. Will be fun to see what that is.
Speaking of firmware, its so nice to have a DAC that is alive and improving. And due to FPGA I think even sound can be changed (not that it’s needed, it sound excellent already).
I am very interested in buying this unit but no reseller in my city so not able to listen might have to go for a 2 hour drive. Lets see maybe someone here has experience I need.
Presently have an Allo Katana which uses an Sound Quality board and is connected to a decent R-Core LPS. LPS powers both the Pi and M/C board so sounds better without using a Isolator.
My plan would be to use the RME with a Allo Digione Signature using a standard Pi (already own, was disappointed with DAC in my AV Preamp).
Regardless enough background is Anyone using the RME ADI-2 with a Roon End point? Can RME do DOP in your configuration? If so what do you use? Know DSP has to be off for DOP.
My long term plan is to add the Allo Usbridge Sig with the ADI-2 once drivers mature.
Thanks
