ive owned X-FI cards, and an X-meridian and i find the meridian streets ahead of the creative cards, (i actually really liked the X-FI cards, until i heard the meridian at work),
as for gaming, the x-fi cards with the later versions of EAX is usefull for playing FPS games (if you take them very seriously that is) as the EAX pinpoints sound events well, but earlier EAX also pinpoints sound, just without the filters associated with later iterations,
now for other types of games, PLIIx achieves ambience and spot effects with aplomb, and for real imersion, headphones are far superior, and in this respect the Dolby headphone technology with the auzentech cards is (in my opinion) better than creatives CMSS-3D, (tho both technologies are good!) and the analogue output on the meridian is far superior, and so sound thru headphone is better!
aside from gaming tho, the X-FI is hoplessley outclassed by auzentechs meridian!
Why?
the analogue inputs and outputs are in a different class, using far superior opamps, dacs etc, and the DDLive, DTSInteractive, encoding in conjunction with the spdif (combo coax optical) input, output, is fantastic, with a quality surround system at the other end, any audio signal from 2 ch, to 7.1 ch, is instantly converted into a DD, or DTS bitstream, for decoding by a external 7.1 system, and the quality is excellent, also the single cable for all signal types is very handy!
basically the ONLY reason to buy an X-FI is for EAX5, because the auzentech card simply does everything else better! and the auzentech drivers are a breath of fresh air next to the creative ones, small and functional, rather than bloated, and style over substance!
also the X-FI connectivity is useless, they use custom connectors, (3 and 4 pole 3.5mm jacks), and combine outputs and inputs on the same connector, eg spdif out, line in, and mic connection, and you can only use one at a time, (the spdif will only output bitstream passthru signal,) unless of cause you buy one of their little but expensive I/O modules.
and the only way to output (true) multichannel audio is thru a creative custom cable, only available from creative)
the auzentech card uses standard connectors thruout, so you can make, or have made any cables you need, or buy quality cables off the shelf, to any length or spec!
anyway im gonna stop with the speech, but to reiterate really the only reason to buy a X-FI card, is if you can not live without EAX5, but remember a propper 5.1(or 7.1) game encoded with DDlive or DTS interactive, and played thru a quality 5.1(or 7.1) system, will ALWAYS be much better than any version of EAX, be it 2, 3, 4 or 5!
and thats that!