I can give you ideas on how to get closer to his tone, but as to what settings he used, there is not a magical way to get his tone. On Vulgar I think he was using the Music Man Stingray. His tone on that album really cut through in the upper mids (750-2khz) and he was a bit absent in the 500hz range. After Vulgar, I know he started using various distortion/overdrive pedals mixed in with his clean tone. He focused a good chunk of his attack in the midrange 500hz to 800hz since Dimebag's tone did not have much sound in that range. If any.
On your 4 PRO, start with the EQ sliders at the neutral setting (tone knobs doing the same thing), try boosting the 600-800hz range on the EQ sliders, use roundwound strings, play with a pick, and don't bother boosting over 5khz. Keep your low mids in check (150-300hz on the EQ sliders set to no boost), maybe a slight drop at 300hz, set all other knobs at noon/neutral, and lastly, roll the low end downward on the 33hz slider as necessary to tighten the tone.
I used to own the 4 PRO and you need to watch out how much low end that head is putting out. At modest and/or neutral settings, the low end is BOOSTED. Oh, that Ultra Low knob, don't use it! I am going to nick name it: "Anti-Pantera" knob. After Vulgar, Rex focused more on shaping his tone to mesh with Dime even more. It allowed him to sit int he mix well and it never ran over what Dime was doing. Hopefully that will get you in the right direction.