When looking at the 987 Boxster Product Information guide and PET parts catalog, I saw that for 06 "The Boxster S uses a high-performance manifold which facilitates an improved gas cycle for significantly higher output." This is a direct quote, including the use of bold, from Porsche's Product Information guide.
In 2007 all Boxsters went to the Cayman style manifold/headers. The Cayman part looks identical to the lower-performance "Standard manifold." The P/N's for the left/right high-performance manifolds are
987 113 106 06
987 113 105 05
I suspect that the Porsche 987 Boxster S "High-performance manifold" would provide improved performance for the Cayman, too. It's available from Tischer's online parts outlet for $1714 a set, not much different from aftermarket headers. Presumably one wouldn't have to worry about failed cats on the Porsche headers.
Does anybody know why Porsche stopped using these high-performance headers??