It would be very simple to put the auduino code inside the illutron and switch between the two using a push button.
The Auduino does not know or care which pin its output goes to so just use whichever one the illutron uses.
The easiest way to do this would be to have
Loop() If auduino pin is high Auduinoloop Esle Illutronloop
And do the same in the isr
Isr If auduino pin is high Auduinoisr // change the output pin to match illutron Else Illutronisr
This way you have very little code to change, you can even keep the setup function exactly as it is on the illutron, this will work provided you remember to change the auduino isr to use the same pin as illutron
Rushed explanation, getting family ready to go camping, hopefully makes some sense to you ?
The code in the link i posted allows you to calibate the channels simply by moving the transmitter through its full range - ie you wiggle the controls and it remembers the min, max and center. If you wantbto change setups you press the programnbutton, wiggle again and it will remember the new set up.
To use vthis all you would need to do is replace the code inside the if mode == RUN partbwith your codevfor the lights.
If you like the sounds that makes, here is a very similar but slightly more complex approach that make a far more entertaining set of sounds. Justvbe very careful what you connect your DAC output to, a few of us have burned them out.
More power to the internal motor allowing it to move to position faster and hold its position with greater torque. Most servo packaging advises that performance will be better at 6volts, but servo life will also be shorter. Your choice.