What experience do you have using Retroarch ? I think PSX and PSP in this build use Retroarch cores to load the roms. If thats the case then load the psx core via Retroarch and enter core information via the retroarch menu. It will show what bios files are needed and rom extension to run games.
Thank you, I went into retroarch and was able to select 2 available cores for psx. None of them worked, but i was able to download pcsx_rearmed_libretro.so and it worked. Graphics are a bit harsh though. Default core that ES points to is mednafen_psx_libretro.so. So I switched it in es_system.cfg file. What rom files does the default core run? As you said "It will show what bios files are needed and rom extension to run games". Where? When I went to load a file it did recommend a core for it. was that what you meant?