check out pypes exhaust (www.pypesexhaust.com). They have a good catted, stainless, X that will fit with your shorties. I have their catted X on my car and like it.
I have mac shorties and a seemingly rare Magnaflow Stainless catted H-pipe, needed it to pass my final emissions test. Now I want a Pypes o/r Stainless X-pipe.
i will warn u now...stay away from anything made by pypes! There fitament is crap! I just put on pypes catted x-pipe and violater catback and am already looking new systems. The hangers on the catback are too long causing the flow tubes to hang low and the x pipe has no hangers. Had to have an exhaust shop rehang everything just to make it driveable because there was like 1" of ground clearance!
All shorties should come to the same spot, so them being Mac shouldn't matter.
With that said, any 2.5" catted H should fit perfect (well, should fit, perfect depends on a lot of variables). Bassani, Magnaflow, BBK, etc... I would assume anyone that makes a catted midpipe will fit.