Dexcool is very close to G-12, so in a pinch it can be used along with the all makes/all models type of dexclones. I've converted my 03 A6 over to Prestone AM/AM recently.
With an 08 Audi, it probably has G-12+ or G-12++ both of which have low levels of silicates. G-12 did not have silicates. Silicates are the acids that protect immediately after a full flush.
Your best bet would be to test the protection level and if it's good enough you can just top off with water until the proper G-12+ can be obtained. If not, a dexclone can be used in the short term, but a full flush should then be done to restore the G-12+.
G-12 will be light pink in color and G-12+ will be a darker violet/pinkish color.
G-12 can be found at most NAPA stores, and G-12+ can be found at Bumper to Bumper/Auto Value stores. Both are Pentosin brands, not the OE Audi stuff.