Hi Pool
I use EM172s with 9V bias all the time. As Willndmb mentioned these capsules can be used with a higher bias voltage than 5V.
These capsules are very quiet and also pretty sensitive. I don't think you will have any trouble plugging the output of the battery box into the line input if you are taping a rock show. If it is too low you could try turning off the PIP bias voltage on the M10 if possible and plugging into the mic input.
Miq