If anyone is interested I did get to the bottom of this. The Nektar Impact LX61 Sonar integration is fully compatible with Sonar X3 and later. Nektar support are going to update their download site.
I needed to factory reset mine because I mashed some buttons accidentally and screwed some settings up. Generally didn't know what I was doing
I needed to better understand Instrument Mode vs Mixer Mode etc to work out what was going on. Now I have unlocked a whole lot more potential I never realised.
I also removed and reinstalled integration files to clear up some dodgy settings.