What's the downmix recipe that PP uses? It seems to attenuate by 5-6 dB

Lo=L+ 0.707C +0.707Ls

Ro=R+ 0.707C +0.707Rs

is standard downmix equation. 

PP implementation seems 5-6dB quieter, with the surrounds reduced. 

Also the 5.1 Mixdown type setting (Front only, Front & rears etc) is only taken when PP is restarted