The big suppliers of catback systems are: Borla (what I have), SLP (the same guys who made Firehawks and SS Camaros) and MSP.
You can also go custom and just redo mufflers. Since the stock pipes are stainless and decently sized, most people just delete the Ubend near the rear O2 sensor and replace the mufflers with some higher flow ones (even tho the stockers are pretty dang good already). Maybe throw some new tips on there.
Just wanted to give you some ideas. Good luck!
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Regards,
Chew
2007 Sly Silver Pontiac Solstice GXP