Well, i mentioned the RadiCAL system (or something from Brembo, etc) because it would accomodate an even larger rotor for more heat disappation
but it seems like their rotors are internally vented based on the pics here:
Why Upgrade Your Brakes | AP Racing Radi-Cal Big Brake Kits by STILLEN
Sounds like based on your use and tires you are reaching the limits of the OEM braking system and it may be time to step up to a "big brake kit"