Additionally, I have one of these - It's a 20db attenuator cable I got from Core Sound back in my minidisk days. Next time I do a 007 job, I'm going to place it in between the battery box and the M10 and if my thinking is correct, it should knock the signal down enough to use the mic in input.
For open taping, I always have and always will use the power modules. They just work, and work well, sound great, don't take up that much room and run forever on a AA battery. I took the belt clips off and have them bound together with a velcro strap with a piece of thin foam between them. About the size of a couple of packs of smokes. And they work great with the M10's mic in input.
I'd love to see some responses from other M10 owners on what they do when running a similar setup.