some minutes ago I was able to get the x1600 to run with QE and resolution change with iAtkos v7 updated to 10.5.8.
The attached files are a mix of what I've found around this forum and original Apple files.
Often rebooted and tried what was working with each other and finally it worked!

I deleted all ATI* files in /System/Library/Extensions - maybe it's important!
This is for the 71c2 512MB AGP version, feel free to try ...
There you go -> Files
Edit: password is flexstarr

