The codename of the Framebuffer driver you are currently using is displayed in System-Profiler > Hardware > PCI-Cards for example in my current case it says "ATY,MotmotParent"
If you want to use GraphicsEnabler=Yes for injection you would gonna need to change the source code of your prefered bootloader to use a different FB. If you want to try out some different combos it might be easier to change GraphicsEnabler to No & replace it with the latest ATY_Init.kext by netkas (32-Bit only) - just change both ATY,**** in "ATI Radeon 4600 Series" part of the Info.plist to the one you want to try - FBs worth trying on these cards are Motmot, Shrike, Flicker & Peregrine. But as I have been trying quite a lot myself, I don't think you'll have much luck with dualmonitoring + any D-SUB/DVI combination - even with changing this.

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