Trained monkey looking to level up!

[Mammers]

You could change controller to an ethernet one like a UC400eth. (Better than USB) .
Get a couple of IDC26 to DB25 cables. Then use your existing parallel board with it on one of the ports and just change the pin numbers accordingly. You then have a second port for another parallel board if you want to add any other items later on.
Chances are you'd only need to deal with power supplies in the box that's all.
I'm assuming your system is using 5v? that all stays the same.
You'd just need a small extra one to power the new controller. (the UC400eth needs 24v I believe).

That's really helpful, I'll certainly look into this aswell. Thank you.