Thanks for your comments folks.

These songs are jazz standards and use RealTracks which are available on both systems, I'm having no problems with those. The only ones with problems are what I call the "hybrid" files that (in Windows) create an associated ".WAV" file.

Does anyone know what file-type Mac-version BIAB uses when it creates an associated audio track? I hoping I could simply convert my .WAV files to that format, load it into the same directory and things would work.