I have had a few exhaust on my 99 boxster.
You can find clips of them all at
www.youtube.com/gwhand all of them except stock!!
As far as your cats go, there should be 4 on your car, there have been guys who have taken off 2 of them with very god results. If you take all 4 cats off you i think you will have cel issues.
Mine is a 99 with on 2 cats so check the board I know there has been conversations about the cat removals and there should be plenty of advice/opinions out there.
Make it a great day
Gary