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Mike it sounds to me like your leaking boost around the DV itself. Now the only way this happens is the diaphragm is split or the changeover valve positive pressure isnt getting to the DV to hold it shut and stop it opening early and bleeding off your boost back around into the turbo intake. Either that or a boost leak which isn't consistant with your noises really. Have you got drop in air filters or intake ? Makes a lot more induction noise than mine did. I could barely hear my intake or turbos at all. It was a unified roar and go type affair. Yours also doesn't boost very high and its sporadic, sometimes boost is looking ok sometime weak. That either the DV's leaking or the wastegates opening before supposed to. If this is your original DV's then replace 710p and also the vac pipes from the changeover valve all the way past bank 2 and into the Tee and down each side to the DV's. Just in case there is some confusion about the what the changeover valve does here is my quick explanation. 1. Off throttle .. .vaccum in manifold change over valve is pulling the DV's open. This is bypassing any boost from the turbo outlet side to stop it from stalling or surging. This reduces turbo lag when you accelerate again. 2. Part or full throttle the boost pressure inside the manifold is diverted through the changeover valve to each DV to push and help hold closed the DV assisting the spring which is also holding it closed but isn't strong enough to resist the boost alone. (And if you make the spring too strong the vaccum can't open the DV when you lift of the throttle.. Makes sense init). The fact you have weird boost, low sometimes tells me the diaphragm is split on one or more or the delivery of the changeover valve pressure is not getting to the DV (like a broken vac pipe or changeover valve fault. When I bought my ctt it had 0.6bar, replaced both DV's and got 0.8bar +. Infact one was split one was fine.

No. The S calipers are designed for the larger diameter S rotors which will not fit without changing the rear uprights and hubs.

The N75 compares the ambient air to the compressed air from Turbine side (cold side) and adjusts boost accordingly. If you have a leak in the line going to the cold side from the N75 the sensed pressure will be lower than actual and the Turbos will try to overboost for a few seconds then the ECU will detect it, through the MAP sensor I think and will cause limp mode or just plain reduced boost. I had this happen on my Audi RS6 which also uses Motronic 7.1.1. Had just did an engine pull & replace, then had a custom tune and I started asking the guy for a tune with less boost. He gave me a custom tune or two with lower boost but said most other RS6's were using more boost than I asked for and weren't having a problem. I started thinking N75, used a spare to no avail, then used my Snapon video scope and started scoping the lines to the Turbos, they went from the N75 to a Tee then went to each Turbo, one was completely disconnected so the line was using ambient air or something in between due to one side being disconnected. Hooked up the line and all was well. While it was happening it pulled like a beast for a few seconds before limp mode kicked in.