So rather than create a whole new thread, I thought I'd add mine to yours. I really like your solution, although a wall wart that put out sufficient current could work instead of the ATX PSU, but like you I probably have an old ATX or two lying around, so why not?
I currently have a Marantz AV7702 with dual trigger outs, although one of the big threads talks about how one of them has issues commonly, haven't tried it out yet myself. The rest of my amplification system is as follows:
ATI AT6003 (from 3, trigger in)
ATI AT2007 (surrounds, trigger in)
ATI AT1504 (might need for Atmos, no trigger)
2x Crown K1 (no trigger)
miniDSP 4x10HD (no trigger)
Ideally, I'd like to turn my Marantz on/off solely and have the rest turn on/off with it. Even if they all had trigger inputs, that is much for the trigger outs on my prepro. Emotiva ET-3 seems marginal at best and I hate all the added mini boxes in the system (aesthetics I know but still).
So I think what I am going to do is take my old "power strip" that I built many many moons ago for my audio system (used to experiment with power filters in it, as pictured in one of the old photos, but now is just simple power strip) and do something like you did inside this chassis, plus add a relay or two to switch a couple outlets for the Crowns, 1504, and miniDSP.