I have an 03 a6, Just ordered mine, turns out two separate part numbers for pipe before MAF and everything after is a different part number actually found it on ebay about a hundred dollars cheaper then ABD's site. Havent been able to find any dyno's on the thing.
It looks so well made compared to the crap pop chargers everone else is offering for around the same money and it looks like it hooks up to the factory cold air scoop by the hood opening.

 

Hey dude, i just got my abd racing quick flow filter system and maf intake pipe for my 01 s4. it was pretty easy to put on, and it sounds and looks great. but it doesnt come with the hook up for the stock air scoop : ( i thought it did too and i also got mine off of ebay. it also made my check engine light come on.