I can help you with that, just take the "12.flac" file in the R46 sound folder and drag it into the R68 sound folder. And while in game, just press the "-" numpad key just like with the R46, since the command in the sound.cfg file is already put. If you were wondering why the music didn't play with the R68 is because it was missing this "12.flac" file.
If you want to replace the cploop, rename "12.flac" as "cploop.flac", but the music will only play when the air compressor will turn on, and it doesn't happen often.
If you mean the (loop) sound, it will play non stop and that will annoy you because you can't stop it.