Read the mM 4.30.00 thread it tells you how to do it, you will need Captain-CPSX PS2 placeholder installed via pkg and reactpsn to use those types. Psx games put the bin/cue and art in a folder then place them on your hdd0://PSXISO folder and go to retro column and hit refresh for it to be detected.
PS3 CECH-2501A [CFW] & CECH-3001 [OFW]/ PS2 SCPH-3901 & SCPH-7501/ PS1 SCPH-5501
Mod Cobra 4.46 v7.00 w/ E3 Flasher [CFW] & Cobra ODE 4.50 [OFW]/ Mod HDD-OSD [Phat] & Modbo 4.0 [Slim]/ Mod MM3
HDD 1tb [CFW] & 640gb [OFW]/ HDD 640gb & OPL v0.92 w/ 1.5tb SMB