[tx_zstang]

I think you're trying to do exactly what my setup is today:
Mac LT's, high-flow cats, dual pipes al the way (no Y) back with gt take-off mufflers. Also, for complience with Austin-area emissions, I included rear O2 sensors past the cats. Also is a bung on passenger side for a wideband O2 sensor. All piping is 2.5", vs. the 2.25" pipe on the stock setup ahead of the Y. There is not any X or H pipe in my setup.

I got the driver-side tailpipe frm same person that I got the gt mufflers from.
You'll also need 2 muffler hangers for the driver side (all the hangers are the same, so the ones on the passneger side can bolt onto the driver side).

Here's a post in another forum with pics of my setup.

Exhaust Pics - Longtubes and cats - V6Power Messageboard

If your picture of the cats are what you intend to use, you don't want those with air tubes out the side! Just get plain cats...or re-use yours.
You dont need resonators unless you do away with the mufflers.

PM me if you need more info.