Finally able to rent and play a DVD recorded with Dolby digital audio. Played it with Theater TEK DVD player (software which uses it's own audio & visual codecs). The 990 immediately recognized it and TADA! output great 5.1 sound.
"What do you mean when you say "multitrack sources""?
Probably not the correct way to say it. I was refering to AV files with 2.1/5.1/7.1/etc... sound.
"I don't believe the Audigy has DDL (Dolby Digital Live!)"
It has internal codecs for Dolby Digital EX and DTS ES. Or you can use the SPDIF passthrough and alow the 990 to decode the audio. Which is what I'm doing.
Anyway, THANKS folks for your replies
Just being able to write down the specifics of the problem and having a supportative forum really helps!
...as for me, well I'm off to read about configuring 'ffdsow' codecs and the ensuing several hours worth of fustration it will bring.