I just got an '05 A6 3.2 to replace a '99 Avant that was assisinated by a kid with a mohawk who coudln't drive in the snow, but that's antoher story..

Any insight on the advanatages to the 18" wheels? The carhas the sport package and you defiinitly feel the bumps a bit more, is there any thing that can be done to smooth the ride out some (tires?); should I step down to 17" wheels? am I being a girliee man?

the new A6 is or looks so big, 17's might look tiny. try going one size wider keeping the same wall ratio to get more tirewall but you shouod stay within reasonable limits of your stock Diameter and rev per miles. If you go to 17, pick a deisgn that looks big with long flatter spokes that go to the edge, no lip... I think your A6 will "swallow" 17's!
Also tire selection can make adifference. Michelin ar expensive and not the best at everything, but they do ride smooth. just my 2 cents

I personally wouldn't drop down to 17's (but if you do, maybe we can trade, lol). I would look into the following things first:

1. Tire pressure: If you are running the wrong tire pressure (either to high or to low) it can have a drastic affect on ride quality. It may sound stupid, but I would check the tire pressure and make sure it is good.

2. Model of tire:This probably has the biggest impact on ride quality. A stiffer "performance" tire will give you a harsher ride than a softer sedan style tire. I would look into replacing the tires with a less performance oriented tire and following gigi's suggestions on increasing the side wall size.

3. If all else fails, you can try the 17's, but I think that changing the tire will have more of an impact for you than changing the rim diameter. Not to mention that 18's probably look better and will be worth more when you sell it.