Hi David,
If you Audi A8 wheels are "real" then they should have a VW/Audi part number cast into them some where. (probably near the center beside the lug nut holes) If they are "real" Audi A8 wheels then the dealer could tell you the part number for the stock bolts or nuts.  Once you have a nut or a bolt in your hand you could tell what seat they will fit.
The other solution is to get the fasteners you want and have a wheel shop or machine shop modify the rims to fit the fasteners.
George,
'85 Westfalia