Maybe you're right. I've never heard of that before wrt the H/X pipes. I do know that catbacks (which the X/H pipe is a part of) must be Z specific, ie 2=) or 2+2.
Now I believe the midpipe/testpipe an all Z's are the same IIRC.
If you want to be successful in your search for an X-pipe, you'd be better served by updating your profile and listing whether your NA is a 2+0 or 2+2. It does makes a difference. It's also part of the Forum requirements as well.