Has anyone figured out a way to receive the video from the Spark (or other DJI quads) to a standard FatShark pair of goggles ? (or thru a cable connection) - or do we have to use the DJI Goggles ?

You can use the HDMI in on some fatsharks with the HDMI out from the RC. But only on Phantom and Inspire. Unfortunately the spark doesnt have HDMI out :-(

Maybe you can use the HDMI out from the crystalsky monitor to get the spark videos to the fatshark. (A expensive solution)

if your on os then lightning to mini hmdi and then to the goggles works on vuzix not sure about fatshark