I really hope the 1/8" mic input jack can be modded to act as a "line in" to avoid having to use adapters to run a set of mics line in. I know it may sound picky, but why they didn't have an 1/8" line/mic switch is kind of odd to me. I'm thinking along the lines of my SBM inputs.
dB-
i think this might answer your question...
L/M/H mystery solved...
L = Line in
M = Mic in
H = High Gain when using the TRS inputs.
Ahh yes! Consider it my ignorance for not reading the manual thoroughly...

"L/M/H Switch: Sets the operating mode of the 1⁄4” TRS and 1/8” inputs. Use the ‘L’ position for line-level devices. The ‘M’ position
should be used when recording from microphones. The ‘H’ position uses a higher gain stage on the 1⁄4” TRS inputs, which can
help when recording quiet signals or using microphones with low output levels. The ‘H’ position does not boost the input gain of
the 1/8” input."