On this application they pretty much all come with a Y pipe although some used parts you'll want to read the fine print/examine pictures....
Key differences from S1 to S2 is the midpipe or Main catalytic converter. The Mid pipe is chassis specific (length is different) while the muffler section is not.
Point, a screaming deal for for the slip-on need not be stopped by the midpipe as it can be sold and the vehicle specific one bought if need be. Well, assuming its even part of the deal.
Caveat - I am not aware of any "slip-on's" that force you to remove the main cat midpipe in favor of slip-on system "required" midpipe/cat-delete pipe to complete the install. But they may exist.
