I would seriously avoid using the Altium autorouter except for basic IC breakouts. It's a very inefficient autorouter, and if you log on to the Altium forums, the official forums on Altium Live, you will see users have been complaining about the autorouter for years but Altium has not done anything to improve or fix. Try the sample exercise in their outdated training and you'll see what I mean. It routes very ugly and places large amount of vias. It would probably be a big exercise in frustration for an 8 layer board. The Altium autorouter is nothing like the one in PADS or OrCad/Allegro -- those ones work fine, but the Altium autorouter needs to be ripped up and remade from scratch. That's my opinion anyway. Maybe others will have more positive results.