Yes Rivers just treats the files as flac.
They
are just FLAC files.
There's no such thing as an "MQA File" it's just a lossless audio file with additional MQA data in the LSB, similar to how HDCD worked.
Until there's an open-source way to detect and decode the MQA data in these tracks, there's no way for a player to know that it's not just a standard FLAC music file and disable DSP (bitstream) automatically when playing it.
One limitation that I encountered was related to the subwoofer. Since I come out of the dac go into the CP800 with XLRs for 2 channel music I am unable to utilize my subwoofer. I don't see a method to output information to the sub. Running the CP800 in bypass mode so the signal is just passing thru the Pre amp.
You would need to either use the RCA outputs from your DAC directly to the sub if it has a low-pass filter, or take the pre-amp out of bypass mode and have it send a low-passed signal to the sub. (assuming it can do that)
Until there's an open-source software decoder, MQA just seems like a hassle. You're better off buying native high-res tracks.