Using the ALSA drivers, I was able to hear sound using the digifire 7.1 card in redhat. I don't know yet about full functionality of everything, but so far so good. Try looking at
http://www.alsa-project.org
They have extensive linux support for lots of different sound cards.
The Digifire 7.1 uses the Cirrus Logic SoundFusion CS4624 chipset (according to the Digifire 7.1 manual).