I have connected my ADI-2 via USB to a RPi4 with Ropieee XL.
Strangely I cannot upsample within Roon to DSD, 768 kHz is max.
I just wanted to test it for future use with HQ Player and now I am wondering what I am missing.
Thx for hint in the right direction.
Edit: I have activated the „ DSD over PCM v1.0 (DoP)“ option.
I have got DSD upsampling to an ADI2pro via a Pi4 working.
Can’t exactly remember the settings, but I think I needed to make sure the DAC capacities were correct - and then tell roon to upsample to DSD.
Sorry not to be more helpful - but you should be able to make this work.
If you are using the volume control of the dac any DSD will be converted to PCM
Read at page 32 chapter 17
Have you enabled DSD over DoP in Roon as it only supports this mode. If your using usb you should get up to 256 if using spdif only DSD64 is possible. If using any DSP or volume adjustments the DAC will be converting to pcm under the hood. Set DSD direct for pure mode which disables these features, but is no use as a preamp or headlamp when this is on.
Found it, I have to deactivate also DSP volume in Roon.
I thought this would happen automatically.
So now no remote volume control by Roon or the ADI-2.
I I would need a headphone with remote volume control (currently I have an cayin iHA-6). I will have to carefully evaluate if it is worth it. 
Personally I’d just let the DAC do it’s own thing. I didn’t find upsampling brought anything to the ADI myself if anything any of Roons DSP seems to have a more negative affect on it. Might be more than effective via HQ player I suppose down to the choice of processing.
Yes, this was only a pre-test for HQPlayer.
But with all this deactivated volume control I would need a new headphone amp with remote controlled volume. My actual amp Cayin iHA-6 does not have this.
Hmm, I’m probably wrong about this but I’m sure I remember using volume control through Roon when trying out DSD on this DAC. Or at least I can’t see how I would have tested it otherwise without blowing my ears off 
When I have a moment I’ll have a play and see if I can add anything to the discussion. FWIW, I have the ESS variant so there’s less incentive to consider DSD (no direct DSD) via HQP.