I have a good gaming PC with an Audigy 2, decent speakers and a standard 2 in front, 2 behind and subwoofer setup plus mic/headset with speaker/headset toggle switch.

I'm vaguely thinking of upgrading to 5.1 but do not know what it involves or how much of my stuff (speakers, cables, sound card, software) would need to be replaced.

It's not such a straight-ahead decision as a vid card upgrade. CALL OF DUTY made good use of my rear speakers but both that game and SPLINTER CELL (which seems not to distribute sound to the rear pair) took a big frame hit from EAX so I disabled that option. DOOM 3 does not appear to use EAX and as far as I can tell does not utilise my rear speakers. I do not believe HALF LIFE 2 uses EAX. What is the relationship between EAX and 5.1? I'm not a huge audio purist but it does seem that my rear speakers are neglected in most apps.

I guess what I'm asking (apart from the practical question about what it takes to upgrade) is whether 5.1 assures a "surround sound" in all games regardless of EAX. Finally, my workspace is not optimal for speaker-distribution, it's not like I'm siting in the middle of an uncluttered room. I might have some difficulty shoehorning another speaker into a rear space that makes sense.

Can someone offer me some entry-level advice? Thanks.

P4 2.8 Ghz
Audigy 2
Ati Radeon 9800 NP
1 GB RAM
Win XP SP2