GTX 680 second screen blank/black?

Hi,

I recently swapped an EVGA GTX 680 into my system as both an upgrade from a Quadro FX 380 (which was pretty underwhelming) and because it was a lot easier than continuing to fight with the problematic 270x I had initially tried.

Anyway, the core part of the system is:

HP Z800 Workstation
Dual Xeon x5670 6-core processors @2.93GHz
48GB ECC Registered DDR3 1333 RAM installed (12 x 4GB sticks)
EVGA GTX 680 (DVI-I, DVI-D, HDMI, & Disaply Port available as outputs)
OS X 10.8.5

I...

GTX 680 second screen blank/black?