Are you sure? It did not work for me, no matter how hard I tried.
This is copypasted directly from the wiki
PCSX ReARMed looks for the following BIOS image files inside the frontend's 'System Directory'.
scph5500.bin (MD5 sum: 8dd7d5296a650fac7319bce665a6a53c)
scph5501.bin (MD5 sum...
Retroarch willl not be able to identify the latest BIOS. The only BIOS that it can and needs to read are SCPH5500, SCPH5501 and SCPH5502 according to the libretro wiki. I had to have all three of them in my BIOS directory for the PSX reARMed to stop giving me the BIOS not found error.