I had a similar problem, in not getting my Infinity pedal to work. Fortunately, I had a Sanyo 3-pedal foot pedal availabe. Plugged it in and it worked right away.
I asked the same question you are asking and got very long-winded answers, which I did not understand. The bottom line is, my Infinity 3-pedal pedal will not work and my Sanyo 3-pedal pedal will work with Express Scribe.