The General MIDI setting would be in the DM10 brain, not Sonar.
You want to use a map for where the MIDI is going, not where it is coming from.
Here's what I have done in the view below:
Insert Session Drummer. Select MIDI Source Track, Synth Audio Output(s), and Synth Properties Page.
In the MIDI track, Select New Drum Map, and scroll down to Session Drummer 2. Select.
Select DM-6, Ch 10 for input.
MIDI path at this point is:
DM-6>MIDI Track(In)>Session Drummer 2 Map(Out)>Session Drummer 2.
In the view, I am redirecting the map to read note 42 (normally Hi-Hat Closed) to trigger note 46(Hi-Hat Open).
Note: If the DM-10 is transmitting GM, you shouldn't have to do this.
Hope that helps.
Edit: It looks like you made some headway while I was putting this together.
Keep going, you'll get it!