Welcome! The Bay Area is a great place for owning an FD and a WRX. In fact, a lot of the WRX tuners around here have also done a lot of work with FDs (and Mazdas in general).
The Vishnu Stage 1 is basically the Stage 0 plus a turbo-back exhaust. I was at Vishnu a couple weeks ago and they had tons of exhaust sets sitting there. I bet they would hook you up if you gave them a call.