Thanks Travis. That answers some of my questions.
Now to just figure out if the M20+ would be okay with something like 9.9 volts, or 13.2 volts, as in the case of a 3 or 4 cell LiFe battery pack. Oddly enough the M20+ manual I found says it is okay to use a 4 cell LiFe, but doesn't really tell you how to switch the jumper to select a setting on the ESC for it. I assume you could use the 12 volt NiMh jumper position, as there is not worry of overly discharging a LiFe battery. Or you could probably use the 3S LiPo jumper setting as well.
I found some english manuals online. Very handy.
M20+ ESC
http://www.servonaut.de/shop/media/p...gct2h78l62s5r1
SMX and other modules, wired to the M20+
http://www.servonaut.de/shop/media/p...gct2h78l62s5r1
It does mention the speaker voltage differences. Good call.