I solved this by changing my configuration on the mythTV box. I removed my /etc/asound.conf file and changed the default sound device to ALSA:spdif. If anyone cares, I am using Mythbuntu 8.04

Previously, ALSA was creating the output configured per a mythtv wiki.

All is well although I have no idea why the 990 would not play a stream that the Technics would play. At this point, I guess it isn't really important.