The hiss can be greatly reduced or eliminated by putting resonators right infront of the x pipe. For example how the invidia gemini exhaust is designed.

update for hissing sound. Posted video at the end of page 2. Is this about the same hiss everyone else is experiencing?

Yup!
 

Yes... same hiss lol. I have the F.I. non res CBE, with test pipe. Super hiss! LOL I suppose it just comes with the territory ha ha ... Thanks for the video too

For those with a Y pipe and hiss, this may help.
The resonated XYZ pipe.
http://escv.net/motordyne/components...1c4e2b0602.jpg

My ART pipes hiss on Stock NISMO exhaust, but ONLY WHEN COLD. after they warm up, they sound great.

This Y pipe looks great , will this fit on G37s coupe?

Yes.