As the subject states, it'd be SUPER cool if FB2K could present an option to download both the native file AND also an Mp3 transcoded version which would be most appropriate for mobile devices with their limited storage capacity.

The options I'm typical presented with when I try to download one of my high res. AIFF encoded files are for example:

Pick first:: 3.18GB total:: WAV 3.18GB
Prefer PCM:: 2.12 total:: PCM 2.12GB

Obviously neither file size is anything less than humongous on a storage limited phone !
If I'm not mistaken an earlier build of FB2K did give you the option of a (conveniently much smaller file re-sized) MP3 version......