I ran a 2006 A6 Avant with the 3.2 V6 for a few years, and loved it. Great sound, super smooth and loads of immediate power with no turbo lag. I would definitely have another. The mpg isn’t great, I would average 22-24 mpg most small / medium runs, and about 29 mpg on longer ones.
There are lots of well documented issues with the chains going slack and the runners wearing loose, so best to hear the car from cold start and make sure there is no chain rattle after a few seconds. If just for a few seconds while the oil pressure gets up this is okay, anything longer than this could indicate an issue.
overall though a great setup, and I’m sure excellent in the A5.