I see the issue, wasn’t sure which one they were using. If you have schematic or teardown images could you post or PM them?
As far as audio, its an issue we are looking into as well. Besides having a separate transmitter system for audio, the modified firmware supporting a USB mic would be a very clean solution, and given the low data rate for audio, should not impact video transmission much or at all. Alternatively if your video is generated on the raspberry, you could do some sort of visually embedded audio like a QR code in the corner, containing the audio for that frame of video, similar to audio-on-film. If not, depending on what you are listening for and its quality requirements (scientific/full spectrum sound recording, or just an identifying sound like a buzzer) you may be able to bury some lower bit rate, compressed audio into a mavlink message, sent from raspberry to cube, then to the herelink, then via WiFi to a pc to be decoded and played.
If you don’t mind sharing a bit about your application, maybe I can give you a more detailed suggestion. I’m open to brainstorming/bouncing ideas around, and if you do think of something please share