Best to recycle those and get something like an HP/Compaq server power supply with a Gigampz adapter board.
I'm using a single one to power my S1.
Simple, reasonably efficient, and runs my S1 overlocked at 393.75 with no problems.

I have two supplies and boards.  One I plan to use on the S1 full time, the other is for bench testing car amps, stereos, running fuel pumps, etc.
One supply draws about 453 Watts, one draws 460 Watts or more.
Of course, the one that draws more power has quieter fans.
Going to have to take both apart and swap the fans.