I have a combination exhaust on my 993 of both Fister Stage 2 Mufflers and a Fabspeed X-Pipe with 200 cell Sport Cats. Again this is on my 1996 Porsche 911, not a Boxster, I'm posting to relay my opinion and experience with both manufacturers since over the years I have purchased a dozen or more different exhaust set-ups. With the Fisters you send them your muffler and they rework it and ceramic coat it if you wish then send it back to you, not too pricey but not cheap ($480 w/o coating plus shipping), well worth it IMO.
Here's a pic of the Fabspeed X-Pipe with the Sport Cats under my 993, it doesn't do justice to how beautifully they are made: