Indeed - ATX PSUs are soft-controlled, so you'd have to find a way to coordinate them.
I found this:
http://www.xtremesystems.org/forums/...ad.php?t=78807
And this:
http://www.overclock.net/power-suppl...ply-guide.html
Google rules.
http://www.google.at/search?q=multip...utf-8&oe=utf-8