I wouldn't do Spintechs... there are plenty of "obstacles" inside them. Go for anything straight through. You can ask Jody about what happens with the wrong mufflers on a turbo application. (not his fault though, they came with the car...)
The best straight through style mufflers I've ever heard are Borla XR-1. They're expensive compared to other similar mufflers and there aren't many case configuration options for inlet and outlet but they do a good job and sound fantastic. The XR-1 Sportsmans are the "single core" design and are louder than the Multicore versions.
I ran Magnaflows on my old Procharged 353 and liked them, I'm keeping them with the TT LS2.