[CA11] Axiom 9 external GPS

I have semi accurate signal reception from my internal GPS antenna inside my Axiom 9. It's no fault of the MFD, there is shelf with radios and cables above it in a pilot house setting. If I buy an external Raymarine GS150 GPS antenna will it plug directly into the back of my Axiom 9? If not what do we have to do? I have a pole mount on the port side and a radar dome in the middle. Is it better to have the GS150 mounted above or below my radar dome?

Thanks in advance..

Scott