DiagnosisUnknown

OK, this is a bit of a saga so please bear with me. When I bought my '05 A8 Base it had dead TPMS sensors. I bought a new set and took it to my local generic auto shop to have them installed. They installed them and they work. Before I took the car in it rode smoothly. When I got it back I noticed a bit of a shimmy at 65+ MPH, especially when I let off the gas. I figured they must have forgotten to balance the wheels correctly so I took it back and had them re-examine. They worked on it for a long time. They had it for two days. The initial diagnosis was bulges on the interior wall of one front tire. The fronts were getting close to the replacement point so it wasn't too much of a surprise. I had them replace the two front tires with same-same Pirelli 255/40 R19 on the 19" 12 spoke OEM rims. When I picked the car up I talked to the head mechanic. He said they tried all different combinations of mounting the wheels on the car. They used two separate machines to validate the balancing on all wheels. Now when I drive the car the shimying is noticeable in the 20-30 MPH range but not at the 65+ range.
I trust this auto shop. I do alot of business with them and they are very honest. They work really hard to make the customer happy. They don't specialize in Audi though and frankly they very rarely see them. He is willing to take a third look at the car if I'm not happy but I'd rather not take it back without some advice along with it if I can avoid it.
So here's the question, is there anything unique to the tires/wheels on Audi, Quatro, or the A8 that I should be aware of and inform him of?
BTW, the rear tires are the old set and they have ~75% tread remaining.