a genlock cable, is more than a simple straight RGB to RGB connection. (if the cable is long, a buffer/inverter chip is present in one of the connector, used to buffer the ExtClock signal)
There are others crucial wires (like ext clock, ext clock enable and some uses overlay/pixelsw)
From the Amiga side theres no problem to identify them (on the Amiga 4000 manual there are all pins assignements)
The "problem" is to find out the genlock side pin assignements.
Unfortunately i've never owned a Sirius so i can't help :-(
