One thing that bothers me a little about this setup is that the two exhaust streams don't meet, so you effectively have two, separate, 3-cylinder exhaust paths without the benefit of a "balance tube" between them.
As I understand it (and I confess that I do not have a degree in fluid dynamics like my friend Mike, who has parlayed said degree into a quality-control job at Sam Adams Brewery, lucky bastard), most engines benefit from the exhaust scavenging that results from a balance tube.
Just a thought, and intended only as constructive criticism. Kudos to the OP for trying something different, though. 
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2002 Boxster S, 6 speed, Speed Yellow
Flat Six Innovations 3.8L Stage II Track Performer, RoW M030 Suspension, B&M Short Shift Kit, Fabspeed Bypass Pipes, FVD Brombacher "Sound Version" Muffler, UD Pulley, Low Temp T-Stat.
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