I once had a buick gn that had an H cross over welded into the cat back after the down pipe. It actually gave it a really nice sound as if it where a dual exhaust from the headers back which is of course impossible on a single turbo gn.
I could be wrong, but I don't think that the cross over has to be built into the mid pipe. I see no reason why you couldn't just put an H cross over into the cat back after the resonators you are going to install.
2013 Grabber Blue Premium Couple, Auto, FRPP N Springs, FRPP Dampeners, Lund Tune