Z6speed is currently having a twin turbo kit produced for the 6s...its going to be very expensive though, since it goes over 300 WHP+.
Blazen also has a turbo for his 6i MTX, put down around 203 WHP I think? Then he promptly smashed his car into the rear of a maxima, so now its in the shop being repaired.
He's burning through his clutch like no tommorow...so once again, any turbo prices you see, make sure to tack on another 1k for misc stuff like a new clutch, poly engine bushings, possibly new axles, etc.