if you do not get any good responses from the bimmerforum sites, and decide to purchase a new muffler, go to
www.solo-performance.com and give Jeff a call. while they market systems for high performance cars, they do have individual mufflers/resonators that will fit the ti, and come in a variety of "sound" levels, including oem quiet. the prices seemed reasonable to me, compared to other retail prices, and the service I got was excellent. I got a muffler, resonator and new tip----the website has the sizes and prices so you can pick the ones you want. Jeff offered good advice when I discussed my preferences with him. it was shipped quickly, and it cost only $100 to have it installed at a local shop.