brian, weird that can get AMPlifier working, and not SongPlayer.... For what it's worth, SongPlayer 1.60 is more stable for me. Beyond having MUI installed, etc. (a number of different SongPlayer graphics sets on Aminet).
The only other thing, I found that SongPlayer will hang, if the MP3 is damaged... and oddly, even some VBR MP3's can cause this...
I'd also make sure your mpega.library is up-to-date, and you are using the correct version for your processor. I'm also running on an '060 here, so that makes a difference, I'm sure.. *if only I could afford a PPC board....* LOL!