How to install 5th axis motor on a 4 axis motor controller Gecko 540?

I finally bit the bullet and bought a Harbor Freight X2 mill.

I will buy the cncfusion motor mount kit with ballscrews.

Now, I am contemplating on buying a Gecko g540 kit (I will only need 3 axis to start, but would later on want to add a 4&5th axis table, how would I then connect the 5th axis seeing that I only have 1 parallel port which is connected to the 4 axis G540?