You can't back yours up on that fw as you have to be jailbroken before hand. From what I understand is once you downgrade to 3.41 modified pup downgrade to a lower original fw like 3.21 or 3.15. Then upgrade back to 3.41 using a sony fw of 3.41 for your region not the one that comes with the dgf.rar and it restores bluray playback.
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