The master cylinder in the NSX has an internal hydraulic circuit to compensate for F-R pad grip. In other words, the pad compound is the same, but the hydraulic pressure is such that the rear brakes grab less than the front. Otherwise, the rears will lock up under hard braking with equal F-R hydraulic pressure.
When folks install a big brake kit on the NSX with the same F-R pad compound, the brakes are so strong, that they overwhelm the factory master cylinder. In other words, OEM can not keep up with aftermarket. When I first got my B-bo calipers, they came with Galfer pads F-R. One track session showed me that I need proportioning valves. After fiddling with said valves for "hours", I ditched that effort. I called Comptech to ask their advice. Answer - mix pad compounds. I then called Andie Lin while he was still with Carbotech. Answer - mix pad compounds.
The CPP is a harder, more agressive pad than the R-4S. Sure enough, I returned to the same track that I ran with Galfers, and only under EXTREME braking did the rears lock up. So I ditched the prop valves and have been happily running mixed pads for two years with zero problems.
As far as vendors, I go to the respective manufacturers directly.
My motto for boosted cars - going fast is fun; however, stopping even faster is important.