Maybe you already have something better than a speaker selector switch.
This PDF claims "M&STM impedance-matching volume controls eliminate
the need for speaker selector boxes or other impedance matching equipment." It lists a 6-step "Volume Control Operation" set-up procedure.
Perhaps your volume controls are like these.
Please consider this plan for the "other room" speakers:
With everything off, connect the AVR's
Zone 2 Left speaker output to one of the
bundles of wires, leaving the other bundle
Follow the "Volume Control Operation"
set-up procedure. (This seems to require
What might the person in the "other room" hear?
Nothing at all. Maybe I'm just wrong
about stereo. Maybe this "other room"
is part of Zone 3, and is not connected.
Soft sounds from both speakers.
Certainly I'm wrong about stereo.
This "other room" is part of a
monophonic Zone 2.
Soft sounds from just one speaker.
This "other room" is indeed part of a
stereo Zone 2.
A disappointed remark from the living
room. The AVR turned itself off (to
protect itself from the load). Maybe
you don't have "impedance matching"
volume controls. Maybe some of them
are mis-adjusted, and show the wrong
impedance to the amplifier.
What will you get out of this work ?
You can label the two bundles of wires
as Left & Right (or Zone 2 & Zone 3 if
I'm wrong about stereo). That's a big
chunk of mapping and troubleshooting
If the sounds are loud enough, you might
be able to estimate how much power
your stereo amp will need.
Otherwise, your next troubleshooting step
would be to look at a volume control. (I
hope it has two transformers.)
You'll still need a stereo amplifier.