What sort of compression ratio are you running? It mightn't be combustion pressure that blew the gasket, it might be detonating, in which case, you'd actually 'want' the headgasket to be borderline, so it acts as a fuse before you do more permanent damage to the engine. Which would mean the 'real' answer would lie in dropping the compressoin ratio down to a safe level.

Problem can occur where it's detonating, but it can't be heard over the noise of the engine/turbo in general. This _might_ be happening (and I'd tend to worry that it might be if it is a std engine/std compression and 10psi on top.An a12 (by virtue of smaller bore) would be relatively less likely to detonate at the same boost/compression ratio, even more so depending on chamber/piston shape))

Personally, I'd try just a new std gasket on there and running water injection, and see if the head gasket holds up. If it still lets go, it's a gasket/clamping issue, not detonation. A relatively cheap way to test that out without risking breaking bottom end parts.