'04 4200 Coupe Cat problem - suggestions please!

Hi Everyone........ just run into my first potential problem with my '04 4200GT Coupe CC with only 20,000 miles on it.
I had the check engine light come on. I had it checked out at the Maserati dealer in San Antonio and the fault appears to be that I have an overheating cat on the right hand side. The car seems fine and is drive-able right now, however, It seems quite likely that I will have a problem in the not too distant future. There is no way in hell that I'm going to replace crap with crap (ie stock Maserati parts) so what do you guys recommend? I would like to keep the exhaust similar to stock; maybe just a tad louder as the wife still has to drive it too!