If it were me, I'd save the cash and install the ESS kit myself. From what I've read, it's pretty a straight forward install and there are plenty of people on the board with experience. Not to mention the guys at ESS have a reputation for being very responsive.
I don't have any experience with any shops around the Denver area other than BimmerHaus but they've been great for the work they have done for me. I'd be surprised if they have much E90/92 supercharger experience. I'm not aware of anyone in the area with a supercharged E90/92.
I play real sports. Not tryin' to be the best at exercising. - Kenny Powers