Don’t know if this will help. I installed the Synology Community version of FFMPEG then created a symbolic link in the /volume1/RoonServer/RoonOnNAS/bin directory…
ln -s /volume1/@appstore/ffmpeg/bin/ffmpeg ffmpeg
To the ffmpeg binary. Then restarted RoonServer…and bingo! That resolved my Synology Roon AAC playback issue.
Granted you have to the above as root on the synology.
Eric