Do you OC your S1?

I actually run my on an 580W Bequiet PSU (http://www.bequiet.com/en/powersupply/282) with 564W on 2*2 PCIE Connectors and it works fine as long as I doesn't power both blades from the same 12V string.

You only have 444W on your 12V, so it should run in theory, but perhaps your S1 needs more power to start. You can try to underclock it or (what I would suggest) try a more powerfull PSU.