^^ People keep saying that, even though its false...
X-RAM on the X-fi has almost no effect whatsoever in performance. Only a handful of games developed support for it. Maybe back in the days of the Pentium 4 X-RAM mattered, but its a non-factor now.
To me, its all about sound qaulity. The Xonar wins that category hands down (192Khz @ 116dB vs 96Khz @ 108dB) over the X-fi.
The X-fi chipset itself is good (Auzentech continues to prove this), but Creative uses low quality parts to drive down its price, and the drivers are horrific. If anything, the fight is between ASUS and Auzentech, not ASUS and Creative.