Im having a similar problem.
I have a HIS ICEq Radeon 4670 working just fine with SL Retail. But the only BOOT solution that I was able to use is an old netkas PC_EFI. I'm not sure which Framebuffer this boot is using, but no other version (Chameleon included) were successful.
Now I was willing to get dual head out of it, but I'm only able to get output from one of the two DVI's output. Anyway, I'm trying to find a replacement video card.
My only problem is: My PSU is not strong enough for a video card that requires additional power source. I'm not planning to get a new PSU (saving money for a Sandy Bridge Macbook Pro 17"). What would be the best solution that's at least faster than my 4670?
*OR* How can I recompile Chameleon fixing the correct framebuffer that would allow me to use dual head out of my videocard? (never did that)