Here is the basic syntax I am using:

sox old.mp3 -C 128 new.mp3 rate -v 48k

Thus far, I've done two tracks, and cannot tell the difference.
Probably not picking the "right" track for it though.

EDIT: Found a very suitable track, with clear soaring vocals against a quiet backdrop to open with, and some nice two voice harmony. Sounds fine at both 44.1 and 48.0 on my Empeg Mk2 player. Making the tracks available to Tony now (PM).

-ml