From my limited experience, I wouldn't buy turbo kit w/o S/W nor peripherals, way too much headaches unless you really like tweaking it all the time.

I upgraded my Audi KO3 to KO4 and needs different MAF, several S/W update from GIAC and fuel regulator, not to mention cooler spark-plugs etc to remedy surging issue. This is on a car that already turbo (KO3 is smaller than KO4 turbo wise), cant' imagine doing an NA engine to turbo.

BTW, GIAC is a pro company doing many developments on Audi/VW/BMW and it still not plug and play

Then stress on xfer-case/trans cause you may launch the car from stop more often, cause it's fun.

I wonder if it's better/cheaper in long run to go with CPO X6 and get GIAC S/W to get 500HP out of it (no changes in H/W or plumbing)