Hi newbie, I have an A4 and got a set of Vredestein Wintrac xtreme 4 last year on a set of spare alloys. Didn't have much snow but in the ice and really cold days it was like driving in the summer!
I found out about winter tyres by just searching online and found this site http://wintertyrereviews.co.uk/audi-a4-winter-tyres-are-they-a-great-investment/ great advice and I think they have a page for the Q7
Hope it helps and good luck!
Jon