Proportioning valve for rear discs

Sorry, I was my understanding was they didn't use factory stock components but manufactured their own multi piston calipers and rotors, Master cylinders etc...Like Baer, Brembo etc.
Not conversion brackets to run other manufacturers brake components.
I would guess most people are not brake educated and just rely on what someone else who is not also brake educated for recommendations.
You must admit that most questions on any subject on these type of sites are from people who have not done their own research and would rather let someone else do that work for them.
Then they complain because they are having problems and don't understand why.
Just because you tell somebody something doesn't mean they understand what you just said.