Thank you robmcc83 , I really do appreciate!
Based on your earlier hint I went and chosen a different path: installed AEL from a zip file and the desired emulators: snes9x2010 and pcsx-rearmed from standard LE/Kodi repos, then proceeded to define the launchers that called RetroPlayer (at least to my still shaky understanding that's AEL/RetroPlayer approach that none of your 3 alternatives cover).
This worked like a charm for SNES, but for PSX not so much.
I first had the issue where PSX roms would start (although complaining about missing bios) but the buttons would be dead, pads/joysticks funtional - can't even start a game without working buttons..
I can't see where it tells me to upload the bioses, it's showing up briefly on a upper-right bubble when I start a rom, but it goes away before scrolling to show the whole message.
I managed to place the bioses to ~/.kodi/addons/game.libretro.pcsx-rearmed/resources/system and the missing-bios message goes away, but the emulator now core-dumps
In AEL configuration there's a "Check retroarch BIOSes" option that if you point your Retroarch system directory to the place you copied the BIOSes to it checks them and in my case the checksums for what's expecting for PSX (5500, 5501 and 5502) match.
But this is what Retroarch would expect, and as far as I understand I'm using RetroPlayer...
Am I too far in the woods?
I'm not tied to the current approach, I simply chose it as it was looking like the minimal amount of fuss. The fact that it did work for SNES was encouraging..
I'm going to look closely at your options and re-evaluate my approach, probably emulationstation seems best since I've seen it working with RetroPie...