you could try STEINBERG or wavelab. they support 16 streams in one record, so you should be able to edit, remix and so on. a regular soundblaster has a waveeditor addet, but with less functions.
for dj effects you could go for eejay mixer
you can't edit in mp3 format, cuz it does'nt have the needet streams !!!!
you have to edit in wave format, and after storing you need to convert into mp3 with cdex or audiograbber (free)
ciao