From what little I could find online, there seems to be some problems with emulation that causes slowdown and desyncs in the audio department in DDS1. DDS2 is better, but still seems to have some small issues.
Like I said, that's just stuff I read while doing some research, but since there are quite a few problems with PS2-emulation on PS3 anyway, I can imagine that it is true. If it's the only way to play those games for you, I'd still say try them, since they are amazing games, but if you've got a PS2 around and can find a physical copy somewhere, I'd go with that.