The TopSpeed catback exhaust has a mounting bracket/tab above the muffler.
These pics for for an early Boxster with only one set of cat's between the headers (not integrated) and the muffler.
The catback unit mounts to the rear of the transmission using the bracket/tab and then connects to the stock C-tubes. My car also has the cat delete pipes (test pipes) from Fabspeed.
Be forewarned - this setup is pretty loud - to the extent that I wear earplugs - but it also has an incredible snarl and growl sound that is really awesome.
