@gavinb
To convert mp3 to 22kHz mono 8-bit (8SVX) sample:
mpega -s -A "4 Mat - Anarchy Menu 01.mp3" -o temp.aiff
sox temp.aiff -r22000 -c1 "4 Mat - Anarchy Menu 01.8svx"
PS. Some sox builds handle mp3 directly. I think the m68k version doesn't, however, thus going thru aiff temporary file.