With respect to 6V vs. 12V operation, Neal at Grace confirmed to me that you can run either voltage out of the box with no change in the box required. I didn't ask about 9V. They do have a pinout preference on the power cable, though I "think" that's intended as a convention more than a requirement (YMMV). I chose to follow it
From the manual:
POWER SUPPLY CONNECTIONS
A four pin XLR connector is used for the DC power input of the V2. The V2 can be ordered
to operate from either 6 or 12 Volt power sources. Pins 1 and 2 are ground and pins 3 and
4 are either 6 or 12V DC.
To avoid compatibility problems it is recommended that 6 Volt
systems be wired to use pin 3 for hot (+6v) and pin 2 for ground while 12 Volt systems
should be wired to use pin 4 for hot (+12v) and pin 1 for ground. The V2 current draw
ranges from .38A to .62A depending on the microphone used.
The only jumper changes associated with voltage levels are to let the front panel LED's know how to read battery levels accurately.
(Which is what Neal is referring to in the previous post with battery packs having their own LED's for monitoring battery level)
I didn't bother adjusting mine for this reason. The procedure is documented here:
http://www.gracedesign.com/support/v2_voltage_calibration_procedure.html