I just moved from A8N-SLI Deluxe to an Intel system. I was running Vista Ultimate 64bit on the A8N board and didn't have any problems. I seem to remember that Vista actually found a driver by it self, but not sure. In any event, there are no available Vista drivers for the Realtek audio on the Deluxe version of the board on ASUS website either, so perhaps what I did was to download an XP/2003 64bit Realtek driver and installed that.
Give it a try - as I said, on the Deluxe version (which as I can see uses the same Realtek on-board audio) I had no problems at all on Vista.