Hello toleda, I thought I'd drop a note here that might help troubleshoot future users. Using HD7950 and the hd4600 in mavericks, I have used both of your guides and found the following.
If you init the dedicated gpu in bios, with the intel still activated, my display does not report correct resolution, and there is no underscan option on hdmi tvs. On top of this, hdmi only sometimes works, other times it freezes the system.
However, if you go with the route where you init on the internal gpu and your guide where you suugest 0D220003 as platformID (which does not mean you need anything connected to it, your display will come on once osx boots), everything works on the hd7950, hdmi audio, hotplugging, overscan, proper resolutions, you name it.
could just be my exact combination of hardware, but I thought I'd note it down here.