twin charging can and has been done to numerous sti's without determental effects. The Shop i use here in Az (Forced Air Technologies ) has done it for years.
Yep, no doubt they do it, but here's why it works without "detrimental" effects for FAT. Quoted from their web site:
"Forced Air Technologies, Inc. specializes in designing and manufacturing complete turbo systems for all of your exotic and “one of a kind” high performance automotive applications"
The fact that you "use" a shop says they also likely maintain the setup. I anticipate they only sell their parts "installed". Not likely they would piece together a "kit" for someone to install by themselves. Not saying they don't, but it doesn't seem likey they would rest their reputation on someone else's installation work. I'm sure they "charge" handsomely for their work. All said, it isn't a viable setup for more "mass-produced" and maintained applications.