Power Supply Calculations

Ok guys, I'm switching gears on my project and need some help.
Previously, I was going to use some AC drives for my brushless
motors so I didn't need a separate power supply. Now I do
because I recently purchased some WorldServo drives (so I can use
step/dir software) and need to figure out what power supply to use.
I'm having problems figuring it out. My project is retrofitting
a Bridgeport M-head. My motors are probably a little overkill so I
know I don't need to max them out.

Using the formula of Amps = 2/3rd of the motors rated amps I come up
with the following

Motor RMS is 7.5, so 7.5*.6666 = 5amps However, do I triple this
(for all 3 motors) to obtain the whole power supply rated amps
requirements?

The voltage part of the equation is hard for me because I don't
know what motor spec to use to multiple by 3.

Here are some of the specs for my motors:
Stall torque 780oz
Peak torque 2,000 oz
Rated power 1,400 watts
Const stall current 10.6A peak
Const stall current 7.5A rms
BEMF constant 62 volts peak/krpm
Resistance 25c 1.2 ohms
Inductance 3.8 mH
Recommend bus Voltage 320 VDC

Can anyone shed some light on determining what power supply I need?
Thanks a bunch.

Mark