I had the same problem with vice city when I transferred music using Virtual CD Ripper.
Best thing to do is to rip tracks the normal way, it's long and boring but you should work on it with a few mates but only one of your xbox and after you've made a decent soundtrack, transfer to each others xbox.
Remember if you're planning on updating the soundtrack then it's best to do one xbox because if you do one album on one xbox and another album on another xbox, you won't be able to send just that one album because the sountrack information is stored in a database.
Sorry if you already know this but I thought it's best to explain it all just incase.
Other reasons I think it might slowing down is becuase of the bitrate and maybe also the WMA version, I think it's supposed to be version 8 not WMA version 9
Yeah, I'm in the same boat. However, Even when I rip using my MSDashboard, San Andreas still won't recognize my sountrack(s). Either way, no music. The only thing I hear is some really slow, garbled stuff in the background, and I hear that all the time when switching in between radio stations too. The transferred .wma files play fine from both MSDashboard and my PC. Very strange indeed. I will check .wma file version tonight and see if they are version 9 files. If they are I will try converting them to version 8 files and let ya'll know what happens.
In the meantime, if anybody could shed some light I would really appreciate it.