Hi,
I don't think it's possible to control Orbiter's build-in MFD's by joystick right now.
A solution would be to use an external application, that converts joystick axis/button data into keystrokes. Try google, I think there are various programs available for that.
There is another possibility for developers creating their own MFD.
You should be able to use DirectInput or XInput in your MFD code, to read out any HID-device (like Joysticks).
Then, you could use the data for anything, including controlling things on the MFD.
Best regards,
mcduck