The thing about pypes is that there does not seem to be any consideration for the exhaust system beyond the x-pipe. What I mean is that they provide you with collector extenders but that's it; it is up to you to purchase, or god forbid, fabricate, an adapter to your exhaust system. If you have headers, you will need to get adapters that adjust to the width of the collector and possibly, reducers.
For manifolds you may need to cut, bend, and weld or purchase new downpipes to fit. Its unknown from the literature I've seen.
TTI on the other hand requires that you specify manifolds or headers, and what type of headers as well, when you purchase. They provide pretty much everything. You pay almost twice as much, but I'll wager it's a quarter of the effort and frustration.
