Thanks again for the pointers. I checked the .2ohm resistors, and
although I wasn't able to check all of them, one may have been shorted.
It's in a tough spot to get at with the DMM probe (which may have been
grounding out somewhere else), so I'll remove everything from the
chassis. That looks to be a pain, but I think if I'm going to end up
replacing components, I'll have to do that anyways.

The U1 board is the pre-amplifier board (vertical, on the front channel
side of the unit, parallel to the heaat sinks). Your memory is spot on!
I found the offending transistors on the schematic, and will add that
to the list of things to check. It's odd that the circuit protection
would kick in only when the surround board is plugged in. Q3684 was
easy to get to, while still int he chassis, and seems "normal" with the
DMM. B-E and B-C was .2Mohm's (and .6-.8V in diode mode), and C-E
65KOhms and dropping (I see a 56K and a 1K resistor in series across
the C-E circuit). If the muting circuit goes, do all the diodes usually
go? I had everything behind a surge protector, but maybe it was junk.
Anyways, you guys gave me another evening of things to do! Thanks
again.

Andris