[dvldoc]

Many things can lead to a blown head gasket but water injection coming on a few PSI to early is not going to be one of them unless the extra boost leads to a already weak stock headgasket blowing.

And it appears from what I have found The Audi and VW have a weak stock headgasket prone to Premature Head Gasket Failure. If your going to replace it I would go with a Felpro set. Engine out is always easier than trying to do this stuff with it in. If it was just the headgasket I would leave it in. Your misfires were probably coming from coolant leaking into the combustion chamber. You really won't know if the piston rings are bad until the heads are off.