The Termi threads complaining of fitment problems that I have seen with photo's, I noticed that the headers seemed off. The Termi headers go on from left to right 4-3-2-1(must be an Italian thing), not 1-2-3-4 which will throw them off alignment at the collectors. There are no instructions with the full system so it's very easy to make this mistake! I have not heard of any1 having problems with fitment from the Y pipe to slip on - The left silencer seems to kick out a bit. People fart around getting the conical ends to line up the way they want, but that's like some1 hanging a picture on a wall. How much time you wanna spend getting it just perfect?
The STR(street) version have smaller diameter pipe & possibly the sleeve peice your talking about - the COMP version is free flowing with wider elements, but may sacrafice low/mid power for a bigger hit up top on race tuned bikes.
Termi's are sick!
you can get more information by calling these guys once you get home -> www.eurocorsa.com