Personal experience - you want the loudest you can get, you need a Racingline y-pipe to maximize the sound of whatever you get.
If you want a really stable linear sound (only way I know how to describe it from experience) you need a full catback with the y-pipe. This gets rid of any crimped piping in the system (which is engineered into the piping for ground clearance purposes).
The fitment of the Tanabe is great, and the sound is fantastic when coupled with a y-pipe.
The best combo on the 3.5 AC is the Greddy Spectrum Elite with a y-pipe. From everything I've heard, this has the best sound, which I'd describe with a hint of luxury sport. Really smooth and present, but won't drive you insane at cruise.
You want loud? Greddy TiC with y-pipe. That has the nastiest burliest sound. It's borderline straight-pipe in design. The next highest burly sound would be the Borla + y-pipe, and it's second to the Greddy in that you're stuck with the factory piping between the y-pipe and muffler/axleback.
This is my video with my Tanabe and AEM intake, done with a better camera than Tanabe used: [youtube]
http://www.youtube.com/watch?v=jTQv9iJbMik[/youtube]
I'm still working on my videos for my Greddy SE before I got rid of my coupe.