Originally Posted by NeoE46
As I stated before, had both accumulators been Tee'd to the front solenoid, the rear would have been bypassed and full control would reside with the front solenoid. The vacuum signal would have reached the rear wastegate through the yellow hose. This setup, however, would cause significant delay in spool up for the rear turbo, hence the reason BMW designed the system the way they did.
I will keep it simple as I believe you are set in your beliefs. That said, I have taken the DP's off, applied vacuum, tested vacuum at multiple points which none support what you have stated. If you apply vacuum to either tee, both wastegates close. In fact, if BMW designed it the way you suggest, it would be an awful design and I have designed several pneumatic control systems. There is then no fall back. You might as well run a single solenoid like the B5 S4. The dual set up is to provide quicker response than a single could provide while still providing a back up mechanism.
That two inch section of tubing does not act as a buffer for anything. Unless there is orifice plate or sintered filter in between, the vacuum at the tee, and subsequently the actuators, will be the same. BTW, the solenoids role is not to deliver vacuum but relieve it. Vacuum/pressure always balances its self and remains the case here. If there were a vacuum differential, nature will take care of it and make it equal.
FYI, I have removed items, tested and verified functionality as I was considering creating my own product. But there are other aspects of my life which come first and the project was abandoned. Following that I have provided some research on the boost control through testing and have hands on experience with it.