Yes, all CrossFire motherboards will run at 8x8 mode meaning they will split 1 PCIe X16 lane into 2 x8 lanes, this is how SLI works also. The exception to this rule are the new SLI x16 motherboards (nF4-SLI x16) and ATI Xpress 3200 boards which can run both SLI/CrossFire cards at x16 bandwidth, however tests have shown VERY little to no performance advantage using today's top of the line cards, but in the future as cards get more powerful they will start to saturate the 8x8 bandwidth, my opinion is if you really want the 16x16 bandwidth when you upgrade your graphics cards again, if you can afford 2 $500+ top of the line graphics cards, you can also afford a new $200 mobo
so I wouldn't even worry about it.
My mobo (P5WD2-E Premium) has 4 USB 2.0 slots built into the back panel with the option to plug in your case's front panel for up to 10 USB ports I think. You have the 4 in the rear plus 2 USB headers and each header (plug on the motherboard) can supply 2 more so I guess that makes 8 USB 2.0 ports lol. I currently am using 3 of the rear ones as well as 1 header because my case has 2 front panel USB ports and they work great.
PC5400 refers to the bandwidth of the memory, PC5400 means that memory can transfer 5400MB/s of data, whereas DDR2 667 is the DDR (Double Data Rate) speed of the memory, DDR2 667 actually runs at 333MHz (333.5 to be precise, 333.5x2=667) and DDR2 400 runs at 200MHz, DDR2 533 runs at 266MHz etc.
Lastly, I have no idea how the onboard audio is on this motherboard because I have a PCI Sound Blaster Audigy 2 Value which I use so I disabled the onboard audio.
Any more questions? lol.