I believe you are correct, the C series and E series displays are basically set up as GPS Plotters and need seperate control units for any other purpose.
I might be being daft, but what exactly are you trying to achieve? as the Fluxgate compass is usually used to drive another system such as an autopilot or instrument array. The GPS will give you all the directional information you should need.
I can ask at work(Raymarine) but will need to know what you want to achieve.
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