Bruce,
First of all, congrats on your new ride!
There are MANY options for either quieting (or loudening) these exhaust systems. I recently did a lot of research on all the options and actually picked up more valid information over on the Factory Five forum (do a google search for the URL).
There are
diffuser cones available that can be either tack welded or bolted inside the sidepipe (either at the collector or at the tailpipe/exit). There are also other "devices" that can be inserted into the pipe to reduce decibels. Some options just require varying amounts of
surgery, which equals $$.
For me I'm actually going the opposite route of you. I just placed an order this morning through Jeg's for a pair of Dynomax racing bullet mufflers. I'm going to have them welded in place of the factory glass packs on my Superformance. It's definitely going to cost me more to increase the exhaust note versus quieting it down.
Good luck on your choice and let us know how it worked out!
-Deano