Originally Posted By: Serenity_Now
Heres my guess...

Its a 4 pole relay with normally open and closed contacts. Low voltage DC coil (probably an ice cube 12v automotive relay) hence the power supply. The relay input side is the from the amps and the output side is jumpered out and going to the speakers. Very cool setup and custom box! We built stuff like that in motor controls/PLC labs. And yes, I'm a dork for knowing that and posting. grin

You should build a few and sell them.

Apparently this was a prototype unit and there were plans to do a ver2 with improvements.
I don't know if designing some kind of gain control was in those plans, but that would be the biggest upgrade i could foresee.
Otherwise the switcher worked fantastic.
One user could toggle it back and forth quickly when testing say, two different amps, and the listener would never know which amp was playing.
We used this when testing sound differences between a receiver, an old tube amp and a modern Coda amp.

"Those who preach the myths of audio are ignorant of truth."