I just got my ET5 setup after a little trial and error (moved from OpenTrack with an older RealSense camera). I found that if you uninstall OpenTrack this removes some conflict I was having as I had both a TrackIR device and a HeadTracker device being listed. Second thing I found was I had to run Tobii Game Hub as admin on initial install, so the HeadTracker.dll file would install in my DCS program directory. After that you don't need to elevate as admin.
Once I had the above two issues resolved it's been smooth sailing. I've very happy with the tracking required very little modification. I do recommend setting up the hotkeys in GameHub for both Enable/Disable toggle and head tracking reset.
Also to give you greater range of view, while still looking at the screen, I recommend setting your Head Rotation sensitivity for Yaw and Pitch to 2 on up so you can get full 180 degree to check your six.