New Rift integration in Unity5 not working on laptop

Hi,

I am trying the new "Virtual Reality support" in the Player Settings (NOT the Rift-Unity integration provided by Oculus), using Unity 5.1.0f2 (Pro Beta) and Rift DK1.
Everything works fine on my workstation:
After starting the compiled executable the rift gets connected and all sensors work.
I can see a stretched single view cam on the pc-display and the stereoskopic view inside the rift - very nice!

Unfortunately the same executable does not work on my laptop:
Although the rift works fine with older examples incl the provided Unity integration (Tuscany demo) it does not get connected to my new project.

The Oculus Configuration Utility is the same version on workstation and laptop (1.6, Displaydrivers 1.2.4.0).
Checked DK1 Legacy App support.
Tried both Direct HMD Access and Extend Desktop to HMD.

My laptop has an Intel HD + an NVidia 860m graphics card, may this "dual system" cause the problem?
(Disabled the NVidia card in device manager, but no changes.)

Any ideas are very welcomed!
Thanks!
Carsten