RealBand just uses Biab in the background to generate up the tracks and is on the old side of things, you are best to watch the BBPlugin as hopefully at the end of the year it should work in a totally new way and be crossplatform and released at the same time with same features.

You can Crossgrade and use both by just Crossgrading the app/exe only and just convert wma<>m4a or if you buy the Windows Audiophile version you can use it on Mac also as Mac will use the wav files as well as aiff and m4a.