CraigG... I have tried today...
Downloaded 'Core Software with Dusk' (version 5.0.0.4). Got camera connected in SG Pro, could set Gain etc, but the camera bluntly refused to connect in Atik's own Infinity software. Hence this later (with Dusk) version still has bugs. It almost worked in Sharpcap, but crashed at the end of the sequence. Quite evidently, Infinity, SG Pro and SharpCap all perform differently with this ASCOM Driver and Atik has still not resolved this with the Dusk. Hence, that's still work in progress.
So, I again reverted to the previous (August 2018) 4.2.2.9 version (without Dusk) Core Software. The camera now works fine with Infinity. Then, using settings in <Equipment Profile> I was now able to get SG Pro working. I could even set Gain and Colour camera. I have not tested at night, but in this older version Infinity and SG Pro appear to work fine. Alternatively, it could be that my flirting with 5.0.0.4 at least loaded the correct ASCOM Driver. But I think there is a solution for Infinity and SG Pro. I just need a clear night to test properly.
In the version 4.2.2.9 Sharp Cap recognised the camera was connected, but I had to selected 'Atik Camera' (not Atik Cameras). This rather promisingly then offered RAW16 as regards colour or Mono (so it had auto detected it was an Horizon OSC). I still could not set Gain in SharpCap, but I guess I can leave it set in Infinity and then switch to Sharpcap.
Clearly , there is still some work in progress, but it looks as though Atik is very close to a resolution in all software options. But you need to hold onto version 4.2.2.9 for Infinity as at today. My guess is that this will be wholly resolved in a day or so as I know Atik Support is in conversation with Sharpcap.