I have recently been re-watching some of steve's old rig/ gear videos as well as videos about the PIA, and I was intrigued with the devices in the back trem cavity. Having had some experience with many Floyd, Edge and other similar trem systems I am well aware of the inherent tuning stability issues they suffer from. I stumbled across posts and comments talking about the Ibanez Backstop which seemed to help with this problem, unfortunately it has since been discontinued causing me to go hunting for a possible replacement/ stand in.
I've since searched extensively and the closest thing I found to the "Trem setter's" Steve was referring to (which I'm pretty sure is EXACTLY what's in Steves PIA) is the Göldo Back Box
( https://www.thomann.de/gb/goeldo_backbox.htm )
it's pretty much a permanent modification to the instrument but based on what I've seen, read and heard about them is completely worth it.
I hope someone here finds this useful and we can hopefully encourage the industry as a whole to start fitting all guitars with a tremolo with one of these (or something similar or preferably better) so that we can all enjoy the expressiveness of floating trems without terminal tuning problems.