Is there any way to change the music in psx games(eg. like ones encoded in xa audio, etc)? Any tutorials?

use the search, here are some threads going on over how to remove the original audio, once you get that, you should be able to add your own.
I know it can be done in GT, (perhaps 2 too, never tried on GT2 tho) so it probably can be done for other games too.

I searched, but they arent really in depth(unless someone knows a good link to one thread I couldnt find). Anyways, when I mean .xa audio, I mean the one that has like 11-12 songs combined unto one .xa file....