Thanks, Doublej!
I'd actually already started looking at something DIY. Within 20 minutes of my last post, I had an
8 channel 12V relay module and
some jacks on order.
I picked up an inexpensive single channel linear, variable lab power supply recently, so I can use that to inject the output power @ 12V while I experiment, and then go dig something out of the junk drawer to use more permanently if it all works, as well as order a project case. (I always tended to keep wall warts from defunct electronics if they feel heavy enough to have a transformer in them.) If my few minutes of research pans out, I think it's mostly going to come down to tying all of the relay coils together on the same 12V input in a reliable manner - and making sure the draw of those 8 coils is within the range of what my source trigger can provide. (I'll have to pop the cover on my pre-amp and look at the relay it uses on the 12V trigger output.)
As far as I've seen, most 12V audio-video triggers are non-latching, i.e. the gear receiving the trigger stays powered only as long as 12VDC is sensed on the input from the source of the trigger, and the trigger receiving components only tends to draw in the mA range. I can't say I've dug deeply enough into it to make that a categorical statement, however, and I will have some long runs to accommodate.
Good link - I hadn't found that one. Thanks!
