Be sure to check out the Billy Boat 2.5" Dual Single Tips Catback Exhaust System, 6 Speed, stealth version.  The stealth version has center muffler and rear mufflers.  B&B started from scratch to offer a complete high performance exhaust system for the Audi B6 A4.  Billy Boat has an amazing development and research department that assures great aftermarket products.  Dyno-tested, this system was shown to make major gains in both horsepower and torque. Billy Boat assures a lifetime of performance.  And why wouldn’t they?  These systems are built meticulously by hand, out of high quality stainless steel.  This fit's Quattro A4's with 6 speed transmissions.  

Note: Fit's Quattro A4's with 6 speed transmissions

*Stealth version has Center Muffler and  rear mufflers*

Specs:

• 2.5" Downpipe with Flex Joint
• 2.25" center pipe with Center muffler.
• Polished muffler and tips
• 3.5" Dual Single ROUND Rolled-Edge Tips
• TIG welded fully stainless construction
• CNC hangers 
• All necessary gaskets included in all kits
• Reducer included: Allows the customer to connect their factory downpipe or catback to the B&B part. 

Exhaust Sound Examples:

 Stealth Exhaust- 2.5" downpipe with flex joint, 2.25" Center Pipe with Muffler, splits into two mufflers with  3.5" tips