If you are not concerned with recording your own audio tracks, but are concerned with just using Band in a Box live for backing, the laptop's internal sound playback via the earphone jack, connected using a proper mini stereo connector that breaks out to the proper connect to your PA works very fine indeed.
--Mac
First, welcome to the boards, although we're a bit late with that.
We fully agree with what Mac said. We keep our projects simple and use very little equipment other than BIAB (2104 Everything Pak edition). We use Real band a bit but not much as we usually get what we're looking for in BIAB. Good luck with everything!
Al & Di