I installed my prochamber with Pypes high-flow cats today. I am very pleased with the sound. It's not terribly loud, but has a deep, aggressive, raw tone. At idle, it's only slightly louder than stock, but when I accelerate, it has a nice deep thumping exhaust note.
I cut off about 9" of the downpipes and spliced in the cats. My O2 sensors barely reach the bungs on the rear of the cats, but they should be ok. I used some aluminum wire to fasten them to the sides of the transmission. The cats came with plugs for the O2 bungs, so I used those to plug the two bungs on the downpipes. The only real problem I had was that one of the band clamps Pypes sent me was missing the curved washer where the nut goes. I'll get a new one sometime and fix it, but for now, it's holding without it.
Here is the offroad prochamber before modification.
A close-up of a cat.
Overlay of the prochamber and stock H-pipe.
After the modification and ready to install.
Here's a before video.
Here's the after video. (sorry about all the dead space...I don't know anything about editing vids yet)