this is the only bios I saw for your board but I didnt poke around really hard either
0204 2005/11/01 update
Description A7N8X-XE BIOS 0204
Support new super IO
File Size 310.22 (KBytes)
Download from Global USA Europe China Japan
all you have to do is go to
www.asus.com / the select the country you are from from the asus world map / then click on downloads from top of webpage / then from the three menus that will appear you enter
upper most menu = "motherboard"
middle menu = socket 460 from menu
bottom menu = A7N8-XE