Propellerhead Reason is a great complement to Band-In-A-Box IF you work in MIDI, and IF you need a kickass softsynth, and if you DON'T need MIDI out from Reason. (We're still trying to figure out whether that's a bug or a feature.) Note that as of version 6 Reason is a complete DAW unto itself. There are a handful of us here and on the Propellerhead forums who use both BIAB and Reason.

If I read your list above correctly, though, that would give you at least three DAWs (including Real Band). Each has unique features and there is a justifiable use for each, but that's a LOT of firepower, even for an experienced user. Also note that Reaper and Reason each have Rewire and so would work together directly. If you don't know what that means, you need to do a lot more research.

Good luck, friend.

Richard

"My primary musical instrument is the personal computer."