The bypass exhaust can be ordered from Sharkwerks:
http://www.sharkwerks.com/products.php?pid=193

You can contact Darin at FD Motorsports to see if he has some bypassed cans available to send you w/ core exchange or send him yours to get the bypass done:
http://fdmotorsports.net


...I recommend getting both

 

I didn't use Fister's cores. I bought my own set off ebay and sent them to Darin. I'll probably list my stock ones for sale soon.

 

I would go for the modified mufflers first and then add the center bypass if you still wanted a little more.

 

It would be nice to hear what they sound like. I have the Sharkwerks Exhaust so just curious what the sounds is like. I like my Porsche's to sound like Porsche and not some other type of car. Many of the options can tend to change the entire sound of the car from it original vendor.
The Sharkwerks exhaust managed to keep me very close to the original sound but much better. It the Fister's make a big change I would likely remain with my current setup.

 

Well they sound very much like the PSE. I love my Fisters on my 05 997 S, of course I had no center muffler to replace. I consider them to be a quieter exhaust, but then I had fabspeed supercups on my last 911.

 

much better after!