How have you tried booting originals? Are you just booting them "normally", or have you also tried letting the OSD appear and entering into the Browser, followed by inserting the disc and selecting it from the Browser menu? Also, not sure if this would have any effect, but in the case of PS2 originals, have you tried toggling "Skip Disc Boot" in FMCB Configurator and (if turning it off) using the following methods? One could also try going into uLE and using the MISC/PS2Disc option, or by navigating in the File Browser to cdfs: and launching the boot ELF (SLxx_xxx.xx) directly.
Chip-free/MC-free homebrew <3
FMCB 1.93 on MC for emergencies, NA
250GB HDD/FHDB 1.93/OPL 0.9.2 (GSM and non-GSM)/PS2 games, NO HDDOSD
80GB HDD/FHDB 1.93/POPStarter rev12/OPL644/GSM0.37/PS1 games, NO HDDOSD
SCPH-75001 (sitting idle, slims suck):
FMCB 1.92 on MC