FYI: Here's the layout of the stock WRX Exhaust.

(Props to the guy on NASIOC (I don't remember who it was) that drew this up, it looks good!)
FYI: The Vishnu exhaust replaces turbo-back like this:
turbo -> downpipe (no cat) -> mid-pipe (cat and resinator) -> muffler -> tip
the downpipe is longer than the stock one, the mid-pipe replaces bothe the mid and rear pipes, and the pipe for the muffler is way different.[/img]