As you see by my sig, I have an 8.1 with true duals on it, and both cats are right where they are supposed to be. I also have a H pipe in there as well.
You have dual 3 inch running into the stock muffler now. All you really need to do is cut it at the muffler and weld in two aftermarket stainless 3inch in and out mufflers and some tailpipes and you are all set. You need to find a reputable muffler shop that can weld, and bend 3 inch pipe. Should be able to get that done for way under 1,100 bucks.
I didn't use stainless mufflers, I used Dynomax super turbos. They have 3 inch internal tubing and ran tailpipes out behind the rear wheels on both sides. They sound great and don't drone. If you want it louder, you can use a straight through muffler. I talked to Magna Flow and Dynomax, and both of them said that they did not recommend the straight through design on the 8.1, because of severe drone in the cab and highway speed. Something to think about. I took there advice and put on the S-turbos and really like the mellow sound.
My true dual setup with H pipe and all cost around $400 bucks plus crome tips. Shop around, you can get a good sounding setup for much less than 1,100 bucks. I would post some pics, but I don't have any taken of it.