So yea.. my car blew up. Again. (Updated! Read and help!)

[Jeff240sx]

Okies.. here's the problem.
My engine has been in break-in mode for about a month now, working bugs out. I've taken it to 5k rpm many times... where it seems to hit a rev limiter (like the ecu was programed wrong or something). The shop my car is at and I have talked to JWT about idle, hesitation, and the rev limiter and they gave us a list of about a dozen things to check. We moved the MAF about 18" away, and the car idled nicely and stopped hesitating. Here is where I left and have only discussed problems over the phone.
They took the car up to 3k rpm nicely, and then a shotgun-like sound came from under the hood. He shut off the car and coasted to the shop. The turbo is discolored and was smoking, and the headgasket is leaking at cylinder four.
The thoughts were that the engine builder screwed up... but its looking more like the turbo took a crap and somehow the headgasket blew.
Can anyone help me to connect the dots as to what might have happened? My shop is going to tear down the engine and investigate.. but I won't know until at least Monday what really happened.
-Jeff