You can run it on a single 690, even a single 680, but I would not recommend it on a single 680. You won't want to use AA and may need to turn settings down for some games, if not most, but it should be pretty good regardless.
You may also want to take a look at this site that fixes a lot of 3D bugs in games that normally don't support 3D well: http://helixmod.wikispot.org/gamelist