I created that schematic about 6 years ago, you have posted there. My control is the predescessor to the Plus version. So, without a doubt it is correct for my machine. I am using EZ-link with no troubles. IIRC the pins with jumpers are a standard protocol for com ports without a handshake. These jumpers would set each port ready for transmit or recieve. Athough the 25pin on the EZ-trak control may not use 5&20, I have used this cable suscessfully for other RS-232 capable equipment.
You could verify what your 25pin configuration is. If it does not work the first try, you could swap pins 2&3 at one end of the cable. I removed the cover from the control to get the information I needed to create my cable.
I purchased the ends with hood shields and cable through Jameco, but they should be available locally at an electronics supplier near you. Surplus cables can be reconfigured if the ends are not molded on. Remove the case, locate and resolder the ends to reflect the schematic and try it out.