Can I run audio signals through a dimmer switch to control volume?
No you can't.



Figure 1. Dimmer switch triac phase-angle control waveform.

Dimmer switches work using a triac to control the mains voltage. The turn-on point in the mains half-cycle is varied to reduce the effective voltage.


The dimmer works with mains voltages. Your audio will only be around 10 V or so.
The dimmer works with constant mains frequency and amplitude. Audio signals vary in both frequency and amplitude.
Chopping a music signal in such a way would produce awful distortion.


Other solutions:


A stereo wirewound potentiometer. This needs to be rated for the power of your system and isn't a great solution.
Separate amplifiers per room.
Fixed resistors which can be switched in and out.