Need input: Wierd Powerflash behavior

[prc1 <prc1CRAP@xxxxxxxxxxxxxxxxxx>]

I've updated my home theater with a new A/V processor that has 3
trigger voltage outputs.  I installed three amplifiers for the theater
in my basement, and these do not have trigger inputs.  They do have
hard on/off switching with a rocker switch on their front panels. I
had the idea of hooking up X10 Pro PSC01 Powerflash interfaces to the
trigger outputs, then plugging each amp into an appliance switch. When
the preamp turns onand the PSC01's are in the proper setup modes
(Input: voltage, operating mode: C)  the PSC01s send an "on" command
as they're getting +12 VDC on their inputs and the amps turn on.  When
the preamp turns off, the voltage goes away and the PSC01s send an
"off" signal. The amps then go off.  Simple, right?

Yes and no.  The PSC01's are plugged into an outlet strip that's
plugged into the same outlet that the amps (and their appliance
modules) are plugged into.  Everything's on the same phase and side of
the breaker panel.  The amps will turn on A-OK, but will not turn off.

Troubleshooting:  I've used the TEST buttons on the PSC01s, and
everything turns on and off as it should.  I've used a mini controller
and can manually turn the amps on and off with no problem.  I've used
an handheld RF controller and again, everything works. The appliance
modules will respond to the "All lights off" command just fine.  I've
measured the voltage at the PSC01's inputs.  The +12VDC is switching
on and off as it should.

So, why would the Off commands not be transmitted, or why wouldn't the
appliance modules respond if it were being transmitted?  What else
could I try to isolate the problem?
** To respond, remove the crap from my addy...  **