A6 4.2 Upgrades

[4.2A6]

I have an '05 A6 4.2 and I'm finding it hard to find any upgrades that I can make to it. I am really interested in performance upgrades. Can you ever have enough power, or can it ever corner flat enough??? Would also like to make a few subtile cosmetic changes. Right now it's pretty stock. I've added a Calibre Lidar Detector/Defusser. It's a great system if anyone is thinking about it. I've added the Gateway 500, and it allows me to play my iPod though the factory radio. I tryed 2 others, but this is the only one my guy could get to work with the MMI. I've also added 2 12"s and a 600 watt amp to the system, but i might need to upgrade this. It sounded great in my Q, but can barely be heard it in the A6. So hit me up with some info, and "Thanks" in advance.