I had the problem of losing sound on COMM 1 and COMM 2, both in-game and at the SOUNDS screen in settings.
I reloaded my data cartridge (DTC) and did a ramp-start (just got to the set of loading the DTC into the flight computer) and start receiving COMM 1 and 2 sounds. The sounds also returned when testing at the set-up screen after that process.
One thing I noticed at the set-up screen when I had COMM1 or COMM2 test button selected is I would get the sounds when I dragged the volume select bar back and forth.
I’m sure the 3dsounds thing in the command line works for people, but there’s something else that’s actually causing the problem I suspect.