Chris - If the KD8CEC software is working fine for you you should probably continue to use it.
To use our latest software, you would have to either ADD a key jack and connect the tip terminal of that jack to the orange wire from the Raduino's P1 plug (PTT) line (you can easily just connect it to the PTT (ring) terminal on the MIC connector if you are using the provided 1/8" stereo jack for the microphone jack. If not, connect the hand key jack's "TIP" contact to whatever contact on the microphone jack you connected to the orange PTT wire. If you don't want to add another jack, simply wire your key with a plug to match your microphone plug. The key would connect to the ring and round terminals on that plug with the TIP (microphone wire) left open. Simple as that.
Jim - W0EB