It is practically impossible to overload the M10 line input with 4061s. The input can handle ~ 24 dBu (per guysonic); 4061s would generate that kind of signal at ~ 160 dBSPL. Considering that the mics themselves clip at around 144 dBSPL, you'll clip the mics long before the recorder. I can't recall exactly what the usable gain on the M10 is, but I seem to remember reading it is about 15 dB. So even at the mics' maximum output level, you'd still be hard-pressed to clip the recorder. Of course, no show reaches that kind of ridiculous, ear-bleeding level...
I would be more worried about getting good levels, going line-in, without a pre-amp (Sony says the minimum line input level is 500 mV).