I have succeeded in getting the square wave pulse into Max MSP, running it into my Presonus Firebox interface which is included in the project anyway. The Max MSP external object [sigmund~] analyzed the signal perfectly and gave me a consistent hertz value, which needed no smoothing whatsoever. I can also view the square wave signal in the Max MSP oscilloscope [scope~].
It means that for this part of my project, the arduino/Maxuino will sit out. But they have plenty of other tasks as it is...
Thanks very much for anyone who helped, contributed, or gave it thought.
You Tube video demonstrating the results: