Note: Posting in complaints as there's no S6 forum yet.
I have received my new S6 board a few days ago. I power the board via an external +24V PSU. Once I plugin the USB connector, the +5V rail drops to +4.4V. No current is being drawn via the USB port. For testing purposes I have only connected +24V to the board, as well as the USB plug.
Here without USB plugged in, 5.15V average.
As soon as USB is plugged in, Average drops to 4.47V.
For a future revision, I recommend a jumper to select between the internal +5V switchmode supply and USB. This also allows users to supply +5V themselves.