The output level from the mic amps is intentionally low compared to the main outputs, this is so that a suitable overload margin is retained. To use the direct outputs, the record inputs should be re-configured to a suitably lower level, around 26dB below clip, and should be ‘bridging’ inputs; that is, NOT 600 ohm..
The main outputs (and the monitor outputs) are designed to operate at zero level with a clip level at about +25dBu. If you are getting apparent low level on the main outputs, I would suggest that the connections are not correct…. this is an electronic floating output and if the ‘pin 3’ or ‘ring’ of the jack is not connected then the output will look very low indeed.
I have posted this as it might be useful to other users of the M16…… I know that a number of studios use them as stereo sub-mixes for drums…. and to get that transparrent sound, the overload margin is all important!