Ableton shows 16 possible midi channels but you can only use 8 of them - Hermod is an 8 channel midi device. To use them from Ableton > Hermod, set up your 8 tracks on Hermod assigning a midi channel to each track. Then in Ableton mirror those numbers to send midi to those 8 tracks.
Eg: If you have Hermod Track 1 set to receive on Midi 10 then in Ableton sending Midi to Hermod CH10 will trigger Track 1 on the Hermod. The same is true in the opposite direction. Add a Midi Out effect, assign a Midi Channel (eg: 10 again) and then in Ableton set Midi Input to be CH10 and Hermod will control the Midi device within Ableton.
The reason why there are 16 available channels is that is how Midi works. You might have another 2 midi devices within that Midi chain which will use the other 8 channels that Hermod is not using.
I hope that makes sense.