Actually, I just found the answer I needed at the Helix website:

Q. What media types are not supported?
The following media types are not supported:

* RealAudio 3
* Windows Media (wmv/wma/asf, mms streaming)
* Older QuickTime codecs (eg, Sorenson. New QuickTime supported
via MPEG4)
* MPEG1, MPEG2
* Digital CD playback
* DVD

Bummer. So I guess what I need now is to find some Linux player so I
can listen to RA 3.0 files in Ubuntu Breezy Badger. Any suggestions?