My Amiga managed to do half-quality mono with a 40 MHz 030 under the bonnet (Hippoplayer IIRC). The 16 MHz 030 in the SE/30 would most likely not be able to do that in real-time, assuming that decoder isn't much more efficient compared to the MP3 datatype I used for the Amiga.

EDIT: Checked the web site. They're using the same encoder