Do you have a picture of how your car looks now? I'm just curious because most A3s I saw, mine inclusive, had a slight reverse rake. I lowered mine with VWR Sport Springs because I wanted 20-25mm drop only (unlike 35-40 mm drop with other springs) and had to use TT rear spring pads to raise the rear end. And still, my rear end is a few mm lower than the front (depends on fuel of course).
If your front is too low, perhaps you have issues with your current setup (damaged springs or struts)?