Decided to have a proper go at getting my Audigy working in Fedora Core 5 this evening. A bit of googling led me to the linked blog post which in turn led me to the solution. Basically ignore the sound card detection applet in Gnome - it seems to disable anything you've just turned on with alsamixer - and open a command prompt, run alsamixer and then use the '.' button to enable all the options which it says are off (ie. the ones which don't have a volume control), worked for me anyway.