I emailed Tubi USA to see if they were going to make a performance muffler for the 986 and 987.
Here's their response: (by the way it's from Champion Motorsports)
Thanks for your inquiry.
We are currently testing the prototype for the 987 Boxster. We anticipate production to begin in approximately 30 days. We should have products in stock in 60 to 90 days. Sometime next week we will be testing the system on the older Boxster to determine fit. I will send you an email to advise once the test is complete.
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Jesse Hemans
Sales Manager
Champion Motorsport
3101 Center Port Circle
Pompano Beach, FL 33064