i have receiver, connected to sound output of my iMac MB950LL/A.
I cannot switch sound to iMac's internal speakers without unplugging the cable from it.
Can it ever be done without touching the cable ?
Apologies, I did some searching and that iMac model may have the sound output on a hard switch. Annoying. Look for an application called "Audio MIDI Setup" in the Application:Utilities folder and see if that works.