Hey Lance,
I have for 8 years ago developed the same Display.
1. One LED need 2.1V and for maximum Power 20mA. (2.1V x 0.02A = 0.042W)
(16 x 400 x 2 x 0.042W = 537.6W)
(537.6W is absolutly no problem)
2. Lower the driver voltage and you increase your efficency.
I have build a switching power supply with 240V input and 2.3V / 420A output.
(no this is no Joke the sec. coil was cooled with water and the Power Mosfet was IGBT from Hitachi.)
Each segment 8x8x3 had his owne CPU with highside and lowside driver.
(the multiplex dutycycle was 30%)
I can send you a shematic for building this Powersupply !
Sascha