ok, i if you want to put your own MP3/WAV-files in the game all you got to do is this. it's pritty easy but it takes a while.
first of all, i sugges that you make a backupp of your '...\audio\music\'-folder.
then download EA-Sports DittyImporter (originally deisgend for NHL-series, but works just fine with NBA) (http://nhl2002.ea.com/en/Importer.html). then just convert you MP3's/WAV's in the program and replace the original files with the new ones.
what takes so long is that you can't copy and paste the songs (for some reason i do not know what, correct me if i'm wrong though), so if you want the same songs for 'xsong-.asf' and 'xmsong-.asf' you have to do em' one by one (12 of both, a total of 32 files).