I got the X2300 HD working at native resolution with QE/CI on a Gateway C-142XL on 10.6.5 with device ID 0x7211 with the following steps:
- Replaced 0x72101002 with 0x72111002 in ATIRadeonX1000.kext's Info.plist.
- Used 0xED to find and replace all instances of 1072 with 1172 in the Contents/MacOS/ATIRadeonX1000 binary(?). (And yeah, the fact that the first two and last two digits are flipped confused me at first.) It replaced four occurrences.
This fixed QE/CI, but the resolution was wrong, and I couldn't set it. Before this, I was just using RadeonHD.kext which got the correct resolution, but no QE/CI. I decided to try combining that with the newly modified ATIRadeonX1000.kext, and lo and behold, QE/CI at native resolution. The resolution is switchable via the prefpane, too.
I've attached the modified ATIRadeonX1000.kext and the RadeonHD.kext that I use. The RadeonHD.kext ought to work for any device id, if you modify your own ATIRadeonX1000.kext properly.