Yes that sounds like is a logical explanation, I might go switch to an X pipe and see what happens...will probably sound completely different. How would the straight pipes benefit the V8, in this case each bank would have a separate exhaust? Good luck with your set up!!

__________________
2010 BMW X5 ///M
Silverstone Metallic
Black/Black Merino with Black Piano Trim
Premium Sound
Driver Assistance
Comfort Access
High Gloss Roof Rails

Gone but not forgotten: Upgraded!
2003 BMW X5 3.0i
Titanium Silver
Navigation
Cold Weather Package
Premium Package
Heated Steering Wheel
20" wheels (275/45/R20 all around)
Supersprint Magnum Exhaust
AFE Cold Air Intake
Bimmian Chrome Guage Rings
What's A Resonator?