EAX & Other Surround Formats
EAX or "environmental audio" is native to Creative labs and support is very important for a gamer. Basically, this is because it's the standard that game audio has been centered around for some time and should be very high on your list of important features if you play a lot of games.
Do remember; non Creative cards with the exception of the X-Fi Prelude 7.1 will not feature comprehensive EAX support. Most recent cards should also feature fairly comprehensive support for media encoded in Dolby or DTS sound formats.
Some more feature rich cards also allow you to encode content into six or more channels using DTS:NEO technology. However, I have not properly tested this and would suspect it's fairly infantile as a technology at the moment.
It's actually the manor in which the card is packaged that contributes to a large percentage of the final retail cost. This is because some companies use large and often unnecessary amounts of software to separate particular models from others and generally to move products faster.
This can catch the unwary buyer by surprise, resulting in either too much or not enough in the way of software; usually too much. Imagine if your new graphics card shipped with a demo of every new game that the card could play; what a lot of bloatware that would be. Not to mention, it would make all the games seem very similar after a while, which is quite similar to the way audio creation software is distributed. What we get is a flooded market full of hundreds of pieces of software that all do the same thing with different colour fonts.
Ironically, the world standard in recording is Pro-tools and has been for some time. It runs native in Mac OS X, but that doesn't stop everyone who knows a bit of programming from trying to make their own sequencer. It's a mine field for Windows users; that's why I recommend open source programs like Audacity which is a fantastic 100% free recording and sequencing program that can be used with any sound card and is of course completely free.
Right, so what that means is to save your money here and look at basic models of popular cards without all the software. Because truth be told, you probably won't use it yet you will be paying for it.
Look for a basic card that technically meets your criteria with enough features to get the job done, but is slimmed down in its retail form. This could save anything up to a couple of hundred dollars, depending on your needs.
Considering most newer cards come with fairly good support for surround standards like DTS and Dolby Digital, only the heavy users need search for more capability in this area.