It should tell you the voltage range on the CDI ignition module.

The 73" (gas powered) Sbach I'm putting together currently will run two separate 2 cell lipo or life batteries (ie 7.4 or 6.6 volts) through one of these: http://www.hobbyking.com/hobbyking/s...utor_RED_.html as I chose to run twin batteries for the electronics when I have a total of anything over 5 high draw servos (that has 7 including choke and throttle), and a separate 4.8 volt NiMh for my CDI ignition as I opt to keep the individual power systems (motor and electronics) separate. Like you, I'm running high voltage digital servos that can handle that voltage directly, so a voltage step down regulator is not needed.
The beauty of that power distributor aside from being a redundancy system, is that it includes an inbuilt remote controlled CDI optical ignition kill switch, which again I like, and if a company like Redwing RC can offer these same items as well (who I feel strive for supplying quality items), on top of what I have seen others gain from them elsewhere, then I feel safe using them (http://www.redwingrc.com/index.php?m...products_id=82)