Since all the created sessionfiles some how occour an error in the stream while opening and crash. Here the easy way to do it yourself.
(Nach dem alle erstellten Sessions beim öffnen einen stream error melden und unbenutzbar sind hier einfach eine Anleitung)

Have fun with it :)
(Spaß :) )

How to MS master: (LR - MS - LR)

1. Create two Audiochannels (Left Mixsignal and right Mixsignal)
(Erstelle zwei Audiochannels)
2. Create six Aux-Inputs (M and S / -S / -R / L and R)
(Erstelle sechs Aux-Inputs)

Labeling suggestion:
(Benennungshilfe)

Audio 1 = Left Mixdown
Audio 2 = Right Mixdown
Aux 1 = Middle
Aux 2 = Side
Aux 3 = Left Master
Aux 4 = Right Master
Aux 5 = -Side
Aux 6 = -Right

The Audiochannels will provide the Input signal to the MS-Matrix (Your Mixdown). Since you can not create a phisical split of the three signals ( M / S / -S) the Matrix has to be summed directly to LR again. Therfore you have the Aux-Inputs named Left Master and Right Master. It comes in very handy to label the busses with proper names then Bus 1, etc. the picture below shows how.
(Die Audiochannels versorgen die MS-Matrix mit dem Eingangssignal (Dein Mixdown). Da man die MS-matrix nur virtuell erstellen kann muss sie direkt wieder in LR zusammen gefasst werden.)

ProTools Busrouting:

Audio 1 - Input = Non
Audio 1 - Output = M and S (hold "ctrl" while selecting)
Audio 2 - Input = Non
Audio 2 - Output = M and -R
Aux 1 - Input = M
Aux 1 - Output = L and R
Aux 2 - Input = S
Aux 2 - Output = L and -S
Aux 3 - Input = L
Aux 3 - Output = Physical Output 1
Aux 4 - Input = R
Aux 4 - Output = Physical Output 2
Aux 5 - Input = -S
Aux 5 - Insert = Trim with phase reversal
Aux 5 - Output = R
Aux 6 - Input = -R
Aux 6 - Insert = Trim with phase reversal
Aux 6 - Output = S

If it does not work well enable Delay compensation.
(Falls es nicht gut funktioniert schalte die Delay compensation an.

Sincerely yours, S
(Mit freundlichem Gruß, S)