Someone gave me an idea to use CDDA for some of the tracks. I guess that would be the equivalent of ADPCM-B... I think that would work for me and minimise the changes in the code as most of the differences (aside from mute/unmute and stop loop) are handled implicitly by NFX SoundBuilder. Definitely food for thought...Retail NGCD releases often had concessions, so making the cartridge version slightly better for that one thing would make sense. Provided the divergent code isn't a big issue for you.
...but again I will probably defer until after the Beta release. This %!@$# gameplay bug is eluding me!