Richard, funny thing about stereos in an APC:

I drove the command track for the unit I was with in Germany. Being the good commo geek that I was, I had the thing wired for a stereo in short order, but the only way to hear it over the roar of the engine was to pipe it in through the vehicle crewmen's helmets.

There's a switch on the side of the helmet, one way you just talk to the other crewmembers, the other way anything over the audio circuit in the track gets broadcast over the 'net.

On a convoy I flipped the switch to broadcast to music rest of the company.......

And forgot I had the set switched to the battalion command net.

The BN commander was NOT impressed.......but the rest of the BN had a heck of a time.