Maya 2017 - PSD Editor, position driver?

Hi! I have just downloaded the new version of Maya, to take a look at the new tools related to rigging. I have been reading the documentation and watched a couple of videos, and while I can use joint rotations as the drivers for the PSD interpolation, I cannot seem to be able to use positions instead (it is for a face rig), even though there is an option to do so apparently:

http://help.autodesk.com/view/MAYAUL/2017/ENU//index.html?guid=GUID-2AB6C4C3-75AC-4094-A65C-C232739AFB30

Track Rotation: When this is on, the orientation of the joint is used when solving the pose.
Track Translation: When this is on, the translation of the joint is used when solving the pose.

I keep getting the ‘pose already exists’ error, even after trying several ‘controllers’ for my pose. I could build some workaround for this, to use rotations instead of positions, but I was wondering if any of you got to play with this already and can share some experience.

Thanks!