I tried an Audigy 2 Pro card, which includes an optical out and has an option in the driver to output an unprocessed digital signal. I don't mean to argue, as I do not by any means consider myself an expert, but in my experience with the digital out on my old sound card, 5.1 sound did not work properly with external receivers. I had to turn off Doom after a while because it started scaring the **** out of me! The only downside is that it doesn't have hardware EAX, so games take a performance hit when using EAX, but for me it's well worth it for the surround effect. This little beauty has an optical as well as SPDIF output, and uses something called Dolby Digital Live to encode all 5.1 sound so that it works properly with external receivers. I finally discovered the HDA Digital X-Mystique 7.1 card, which is available quite cheaply. Doom 3), did not put out proper 5.1 sound when connected to an external receiver. Also, I found that a number of PC applications, particularly games with 5.1 (i.e.
Unfortunately, all the good digital receivers I looked at did not have an SPDIF input - but only an optical input. I wanted to be able to output dolby digital 5.1 from my HTPC, but I wanted to connect it up to a proper HT speaker system, as most PC based speakers don't really cut it. Just a little tip I thought I'd share, because it took me forever to find what I needed on other forums.