Yup I can confirm it now, the tires I got from Goodyear were horrible! I got a new set of continental extreme contact DW over the weekend and it is finally a real Audi a6 again.

 

I have both 16" and 18" and notice the shacking is considerably worse with the larger wheel. perhaps it has something to do with the larger, softer sidewall on the 16".

I've replaced
tires
wheels (balanced/aligned)
tie rod ends
control arms
rotors

still shaking

I'm thinking it's the wheel hubs/bearing or the steering rack. I've seen cases of both causing similar shaking issues.