For the USB tests, I used a DiamondMax D740X hard drive in a USB 2.0-compatible enclosure and, you guessed it, HDTach with an 8MB zone size.
Here we have a bit of a problem. The USB controller in the Radeon Xpress 200 south bridge is about half the speed of the Intel and VIA solutions, and it uses twice as much CPU time. This may not be a showstopper, but I wouldn't recommend using this chipset extensively with an external hard drive or the like.
ATI's audio capabilities differ from the rest of the pack, largely because of drivers. All the others are using a Realtek codec and drivers from Realtek with support for DirectSound3D and EAX. As a result, they're able to complete more tests, but they're limited to only 32 buffers across the board. It's possible motherboards with ATI chipsets will get Realtek codecs and audio drivers, giving them capabilities similar to the other contenders here.
CPU utilization on ATI's AC'97 audio is acceptable, if nothing special.