My OEM drivers side cat went out so I decided to just ditch the stock Y and run an O/R Y that fits onto the stock manifolds in it's place. I'm running the stock GM SS catback as well. It sounds good, a lot louder than bone stock, it's just that it's on the raspy side at most points in the RPM range unless you're either down really low, or up really high, which can be a negative to most, but I actually kind of like it.
You might want to browse through LMPerformance, that's where I got my Stainless Works from. I'm also pretty sure that as long as the pipes you're looking at are the same size, the differences between the brands would be minimal, if any at all. Maybe a different material would be used or something like that but nothing major.