I would highly recomend the Terminators system from Stainless Steel Systems(SSS) I got mine from stangmods, sound great bolted right on and look awesome with the 4 inch tips.
I ran into the same thing last year. I sold my buddy my Magnaflow mufflers (from catback system) and they wouldn't line up. We had to swap catback pipes too.
Magnaflow didnt seem loud enough for me. They were actually quieter than my stock mufflers. So I decided to get something different. My sss terminators will be tomorrow hopfully!!!
I still have the magnaflows btw if some body is interested in them. Just setting in my shop.
I just installed my Magnaflow catback not too long ago and it went on perfectly. No issues. It was actually the easiest to install set-up that I've ever done on a S197 in terms of how well it fit. Quality is second to none as well. Very impressed.
I was running the Magnaflow Magnapacks welded up as a mid muffler system with a offroad x pipe but with my power level it was ridiculous. I decided to swap the stock mufflers back on to see how it sounded and it sounded decent. I wanted it louder and got the Magnaflow catback and it got much deeper and slightly louder than the stock mufflers. I don't think it's loud enough with 300 rwhp but with the TVS it's perfect for me.
Im planning on getting an offroad h-pipe in the near future, so I may end up going with a quieter muffler down the road. The magnafow does sound good with an offroad pipe.