Yeah, you'd plug the line-outs of the preamp into the line-ins on the Mbox. But you can't use the mic input on your mbox then, so if you thought you could get 3 channels, that's not gonna happen. IDK if the DMP3 has better pre's than the mbox, they're probably comparable. But the mbox only have ONE pre, and the dmp3 has 2. You'd need some kind of outboard preamp for your mbox's 2nd channel anyway. You'd have the option of using the one mbox pre and one dmp3 pre, or using both dmp3 pre's. They could very well sound slightly different, and you could use that to your advantage if you know you want to use the brighter pre or whatever.