Thank you for the info Dave and Jgum.
I have not updated lately because I have been trying to learn C++ and C# programming for the software side.
I did try connecting a wire via exposing the speed wire and splicing it with resistance to the Audio in. There was a lot of noise/interference to say the least and I did not see any form of a square wave which leads me to think that the wire is the enable motor signal.
Today I was doing research on building my own board, but Jgum, when you mention the Mosfet protection... that can be very important as these failsafes protect the user. The last thing I want is a custom board breaking peoples backs, bones, and pride.
I still have not received my 3.5mm Jacks and I have avoided taking the jacks off of my beloved electronics, but I found an old CD Player that I might try to use. Is there any particular way to set this up? When I clip the wire using an alligator clip and run it to the 3.5 mm jack, is there anything that I need to do about the ground? Considering that I would only have the 1 wire?
Dave, I would not know where to begin to calculating the right resistor size. You are right, that it has about 120 Volts AC, but if i remember correctly, everything on the board becomes DC after the rectifier that we installed which is rated at 1000 Volts and 35amps. (We installed it after troubleshooting the ohms on the board and found that the rectifier went bad).
With Jgum's input would you still recommend installing a Potentiometer to try to control it? I have not purchased one yet. I was thinking about buying this (http://www.amazon.com/Digital-Potentiometer-ICs-Step-50kOhm/dp/B005T6CO86/ref=sr_1_5?ie=UTF8&qid=1392928695&sr=8-5&keywords=Digital+Potentiometer) and then using my second Arduino to control it.
All of this info is still overwhelming, but i am trying to hang on in hopes of learning this stuff hands on.