Hi. I'm sorry for bumping this old thread but I found a solution. Using 6.60pro-c , press select and go into Recovery Menu -> Advanced. At the bottom it says Force High Memory Layout. Enable that. Then near the top it says Memory Stick Speedup. I put it on Always. That was enough for me, and my CPU speed is Default. If Default doesnt work then try other speeds. I was having trouble with Diablo (PS1) audio stutter and then game crashing, but now its working with no problems.
did it solved the problem with isos? are they working fine too? and the mp3?