You get headers because you have higher compression...and flow restriction is the LAST thing you want with boost and high comp...so...most likely you started knocking...something got too hot...and POOF! My car ran pretty good on a chipped piston for about 300 miles until the entire skirt desinigrated. Getting headers and moving the powerband up does nothing but good for these cars since they lack top end and have AWFUL exhaust in the first place.

I'm betting on #3 or #4.