What options are available for the 3.6? Do the regular 914/6 mufflers I see advertised work or will I need something with bigger inlet/outlet pipes? Looking for something in the quieter range. Thanks.

Factory 993 headers are 1 5/8", but Patrick Motorsports and others recommend 1 3/4" headers with a 3.6 motor. The limitation is the opening for the muffler. I would call Jim at Patrick Motorsports and get his recommendation. He specializes in 3.6 motors in 914's.
I'm also installing a 993/3.6 in my 914 this winter. I will be running MSDS 1 3/4" headers with an M&K two in two out muffler. It's not a quiet muffler, so I would not recommend it, if you want something quiet.
http://www.914world.com/bbs2/index.php?showtopic=267719

Not sure if you can still get them, but i love my "Laguna" mufflers.
They are from PMS and fit their 1 3/4" headers.

http://www.914world.com/bbs2/index.php?s=&...t&p=2723426

I can make a muffler for a 3.6L

Watching this...

What does the rest of your exhaust look like? The muffler is just the very last part of the exhaust, and you need to take the rest of the system into account when getting one.

--DD

factory replica Dansk, fits perfectly has the same dyno tuned construction as the original factory variety

I would try to find one of Ben's SS quiet mufflers for the 3.6 since you expressly want a "quieter range" sound. I had one and foolishly sold it...