Hi
I used to have the same problem (Mac Mini connected to BV7, connected with DVI and minijack for sound, assigned to PC button) - but I could get the sound through to linkroom by turning linkroom speaker on manually/direct (linkroom speaker stand-by - mainroom playing), and not by remote control in link room. Sorry if that was a bit cryptic... However:
I changed the connection so the Mac Mini was still connected with DVI - but sound was connected via SCART - and assigned it to V.MEM, which work as a charm from linkroom as well as main room.
Hopefully that could work for you?
Best Regards /DocD