Dualing it out is not worth the money. The only way to do a true dual on a straight 6 is by using a split header, which are expensive. May as well replace the cat while your at it. You can get a universal high flow Magnaflow cat pretty cheap from summit racing or jegs. As far as muffler goes, well just depends on the sound you want. Im running a highflow cat and a SLP loudmouth muffler, like the sound but its pretty damn loud.