Almost every other bit of MP3 software I've come across (Winamp, Sonique, libmad, Napster, Audiogalaxy, even Lame) uses the ".mp3" extension whatever layer audio is used

I'm happy to say that with the patch the author e-mailed me yesterday, so does Audiotools. That's the level of support I like: Empeg standard.

I probably favour Audiotools because the guy is prepared to put up with a PC dunce like me with endless patience, but I do find it very user friendly.