**SOLVED**
So I learned that MSFS binds the Mixture axis to one of the throttles. So as it is increased, mixture is reduced, while the other throttle actually controls the throttle. So I removed the Mixture control and all works as expected now, will just have to adjust Mixture through cockpit which is fine by me.
In case you are confused, the X56 throttle is actually 2 throttle controls that can be manipulated seperately our be bound together with a physical 'pin' so they move together as one.
Happy flying!
