Actually, now that I think about it a bit more. All you really need is a "laser off" signal so while the laser is on, there'd be no chance of the laser control signal effecting the mirrors. You'd still need the laser off signal to be fairly specific though so that unexpected mirror movements don't weaken the laser. Also, with a laser pulsing functionality, the scan path of the mirrors could bby CharlesNeville - Polar Machines, SCARA, Robot Arms
Turning the laser on and off with a minimum of cost. There are many bands of audio in the speaker output that aren't useful for controlling the mirrors. They can be used for other control signals. To turn the laser on and off, you could inject a low amplitude, high frequency signal; eg 18kHz, -20db into the output of both L & R outputs. This could be filtered out with a very simple notchby CharlesNeville - Polar Machines, SCARA, Robot Arms