To follow up on my previous post about the fitment issues I ran into with the Pypes X-Pipe, I had sent my previous one back to them because essentially the cat connections were too large. When clamping it down, it crushed the pipe and caused it to leak.
It took them nearly 4 months to replace the X-pipe, but they did redesign it, now including small inserts for use with the factory downpipes. I installed the new X-pipe with the inserts and on first fire-up, no leaks!
My guess would be that the X-pipe was originally intended for use with their catless downpipes, which may be slightly larger than the OEM cats. With the new inserts it sealed up perfectly. Actually it seemed a bit quieter than I remembered, probably because it doesn't leak, and the sound with the Roush axleback is glorious.