Carl,

if you create the song in BIAB, then reopen the saved file in RealBand, all of your parts will be on individual tracks... which can be muted or enabled one at a time or in any combination.

And since RB is a sequencer, Playing the songs through Real Band also gives you the opportunity to send MIDI to other devices if the need should ever arise to do that.

If you want to start out with the format that gives you the most options going forward (so you never have to switch horses in the middle of the stream) I think RB is the perfect hybrid between BIAB and plain audio files. It allows you the ability to include audio and/or Midi, keep individual tracks or merged tracks, you can use it for recording and/or playback.. it's the closest thing to a one-stop musical solution I've found.

If you decide later that you want to use MP3s, just export the songs as MP3s! Easy as that!

my 2 cents. I don't see where RB obstructs any future direction you may want to take. (And it directly imports anything you create in BIAB! How cool is that? No other sequencer does that!)

https://www.dropbox.com/sh/ey71h8ep047758h/AAC12jNM0Hz9Q8zsh5iDeqNHa?dl=0