@Carl do you have ident test disk/files?
I just downloaded all these files from https://github.com/sfiera/flac-test-files
The results are following: (my avr has 5.1 speakers); while doing playback of these files via roon each uses Channel mapping to 7.1, only surround71 is playbacked without mapping.
stereo.flac - no sound - no idea why?
center. -> left/right ok, fc is playbacking via sub instead of center ie ISSUE
quad. -> all ok
surround 50 -> fl/fr/ rl/rr OK, FC (center) goes to sub ie ISSUE
surround 51 -> FL/ FR ok, FC -> goes to sub ie ISSUE, LFE -> goes via center ie ISSUE , RL/RR are OK
surround7.1 -> FL/FR, FC same issue as 51, LFE same issue as 5.1, RL/RR OK, SL/SR ok but goes via RL/RR
Then i made another test so i playback all these files via Kodi which is also installed on the vero4k which is acting as roon bridge and results are as follow: all the tests passed OKAY
Now question is … where is the problem 
is the channel mapping in roon broken, or is the issue on vero4k where roon-bridge app is not able to output correctly via hdmi?
I am also listening some 5.1 flacs and i think it works fine … so im totally confused…