I think i found an error. In isofs.c in isofs_ReadSect, there's determined which part of the .iso to read the data from. It checks if it should read from the 1st 4 GB or from the 2nd 4GB. Well the problem is that DVD9s can hold up to 8.x GB and i have seen that PAL Champions of Norrath is supposed to be 8.02 GB and USA Xenosaga to be 8.05 GB. There may be other(bigger) DVD9 games, as the TOC lists i found looked pretty old and incomplete.
I know the new module will load in another way, but i think there was some talk about keeping the old one as backup.
Tomorrow i will have some time to write the code how i think it should look.