I am having exactly the same problem as in this post.
It was closed saying the problem is solved but not really describing the solution. So the solution seems to have something to do with deactivating some digital outputs. So my question @sgb, @john, is deactivate which digital outputs exactly (and how)?
For example, DSD256 is being immediately down sampled to DSD64.
Press the Settings Icon an choose then Audiosettings and In-Out setting on the RS150B.
On my RS150B one of the output choices where activated (coloured gold and had a checkmark).
When I turned it off, I could upsample to DSD256 in the DSP in ROON. But that was a short success. Next time ROON reverted to only upsample to DSD64 even if all the digital outputs are turned of.
Now I realized that I have a HDMI cable connected to my TV on the digital output. I pulled the HDMI cable from the RS150B and restarted ROON and now I am back to upsample to DSD256 on ROON.
So what I learned is that you can’t have any cable (ex HDMI) connected to the the digital output of the RS150B if you want to upsample to more than DSD64…
To deactivate an digital output that is activated (goldcolour and checkmark) just touch the icon and confirm. I suppose that goes for all the digital output.
Interface a bit quirky if you haven’t seen something similar but it does seem rock-solid with roon once you get it working. I have pretty much abandoned SOtM and Mark Levinson because of varying degrees of flakiness and dropouts with roon. Highs seem slightly rolled off compared with what I normally go for but it is really very very subtle and I haven’t played around with all the filters yet. Fabulous screen.