@mitu thanks for replying .I was trying to get the x68k emulator swap-disks to work rather than the retroarch's . its odd that there are not any info about it on the internet! it got to be a common issue. anyways I gave up :) its seems retroarch is a much easier option now.

thanks again.your guides on this website helped me alot with the whole retropie/launchbox thing . I appreciate it.

I should note that I found out with Resident Evil 2 it is a 2 disc game, but depending which disc you start with depends on the character/story. You still need to swap with the other disc part way through. For this I have combined them both discs twice, so two PBP files, one going 1-2 and the other 2-1.

You should have a 'Disc Control' menu in RetroArch when you open the RGUI menu, from where you can append a new disc, then eject/load insert the 'virtual' disc tray to load that disc. It's described also in https://retropie.org.uk/docs/Playstation-1/#multi-disc-games, but your version is a bit old,so the instructions might not match.

Thanks!

@supercatfooz Update: I just found an HDF file that seems to work fine, making the two .dim files I have obsolete. I'd still like to know if multi-disk mounting is possible for the future, though! (plus it'll help whoever else happens to have this problem)