This $3897 gaming and graphics system justifies its high price with lots of speed and excellent expandability. Peer through the window on the side of the MTower 64's black-and-gray midsize tower case, and you'll see components common to many other systems we've reviewed. But Xi seems to have found just the right hardware recipe to create a screaming-fast PC.

Equipped with a 2.4-GHz Athlon 64 X2 4800+ CPU, 2GB of DDR400 SDRAM, a single EVGA E-GeForce 6800 Ultra graphics card, and two 300GB hard drives striped in a RAID 0 array, the MTower 64 AGE-SLI produced a WorldBench 5 score of 130, the highest yet.

Gamers will note that on our standard graphics tests, which run Return to Castle Wolfenstein and Unreal Tournament, the MTower 64 achieved 280 frames per second, the second-fastest rate we've seen. (The fastest was 283, posted by the Polywell Poly 939N-FX55.) On tests using Doom 3 and Far Cry, designed to gauge high-end graphics capabilities, the single-card MTower 64 AGE-SLI was even more impressive: Its frame rates beat out the dual SLI systems at both 1024-by-768 and 1600-by-1200 resolutions on Far Cry and at 1024 by 768 on Doom 3.

When you're ready to turn this system into a dual-SLI machine, it can be upgraded to full SLI status by adding a second EVGA E-GeForce 6800 Ultra graphics card to its second PCI Express x16 slot.

The MTower 64's case feels a bit cheap, given the system's price, but the interior is well organized, uncluttered, and easy to access; two big thumbscrews hold the cover in place. The two empty hard drive bays and three empty optical drive bays are easily reached, as are all of the expansion slots and RAM sockets.

Getting the motherboard's onboard sound hardware to work properly required us to flash the system BIOS twice, a bug that should be fixed by the time you read this. Currently Xi is offering free Audigy sound cards on new units as a way of bypassing the problem. When we did get the audio working, the Logitech X-530 speaker system sounded great. The five satellite speakers were crisp and accurate, although the bass from the subwoofer seemed slightly distorted at high volumes.

Small (6.8-point) type was readable on the ViewSonic VP191b flat-panel display but wasn't the sharpest we've seen. Likewise, colors were realistic, but they didn't jump off the screen. The control buttons on the front of the display were hard to read and easily confused with the power button.

The Logitech cordless keyboard and mouse are a plus. The keyboard has a sturdy feel, solid key action, and comes with lots of programmable buttons for launching programs, going to Web sites, and controlling your sound system.

Upshot: This very fast, expensive PC with an SLI motherboard will appeal to hard-core gamers and graphics enthusiasts who have deep pockets.