madda wrote: dabmeister : I know about that but the only think what I need it's get my project to computer in .wav format ... I have no idea how to do it ... I know it's a silly/newbie question ... I'm counting on your help guys !
Thank for respond 
Errrr, I don't think you really understand the concept in its entirety. Forget the exception of a basic consumer soundcard and think of a multi input pro audio card with 1/4 inch jack inputs and possibly coax & optical I/O as well as midi I/O.
You'd then would be able to with the assistance of daw s/w, sync the mpc via midi time code or midi clock and record your audio performance from the mpc into the daw program.
Presto, you've got your .wav info secured on the hd (well, ram actually) and saved until you're ready to export it to another medium. Once you've exported it to something like soundforge, wavelab, audacity or whatever, you can do whatever final editing then do a "save as" to mp3. Simple enough.
If by chance you don't have the pro audio card thing going for you, then use a stereo L/R rca to 1/8" balanced male audio cable. You'll have to get some 1/4" jack adapters to work with too.
Question, have you been to tweakheadz.com and checked out all the wonderful info for newbs yet?