I am really picky about exhaust sounds too. Mine is all still stock but I am looking forward to hearing what a new y and b pipe set up sound like. "audtatious" from here has one he is getting installed soon. He is keeping the stock muffler and tips. This is something I am looking to do in the future as well and what it sounds like will help me decide for sure what I want to do.
Here is something I came across just last night. It is a product called Noweeds. It is a "No-Weld-Electric-Exhaust-Diverter-System." What it does is bolt up to your factory exhaust, and electronicaly bypasses your muffler, making it loud or quiet, which ever you choose. It's basically an electronic exhaust cut-out. Here is a link to the Noweeds website. It looks really interesting.
For more information go to
http://www.noweeds.net
It has one pipe going to the muffler when the other is closed and when that one is closed it has a straight pipe. Pretty neat too that you can adjust the sound of your exhaust at any given time!