will the rsr down pipe fit with the HKS hyper cat back? thank you

It looks like it should fit. Make sure they have the corresponding 3" flanges. I looked up the RS*R downpipe and it seems to have the 3" flat flange, and from the small pics I've seen of the HKS Hiper catback, it has the flange as well. You may want to double check, but they look like they'll work together.

Yes and no. It will not fit without the little adapter extension that is heavy in my opinion. If you have that piece, you should be fine. If you don't have that piece, look elsewhere. I have both the RSR downpipe and exhaust. Loud.

San