Scott, that's a good little mixer. Be very careful plugging and unplugging the power supply. I had two of them break. Other than they worked fine for years, as long as you don't need extra ins and outs.
Regarding the Harmony M, there is a procedure to assign the midi channel and the zone from which the unit reads chords. You have to have the owners manual in front of you and follow it closely.
I have used it with a couple of Rolands and a Yamaha and it worked good with both after setup.
DonM