Music off, sound on all machines.

Main reasons being:

1. The sound can give and additional indicator of your alts being attacked/sapped/poly'd/etc that you may not see straight away on your main monitor.

2. You instantly know if your alt gets a whisper (like from a GM maybe )

3. The fact that the sounds are slightly out of sync makes it sound like a small crowd of different people when clapping, cheering, etc

4. Nothing sounds more like impending doom than multiple shadow/frost/lighting bolts charging up...

Cheers,
Stealthy