upload the project, so i can see your routing.
in general i think you have to route each ezdrummer out channel
to different reaper audio channels.
there is an action to do that, in each fx chain window.
fx chain windows -> options -> build multichannel routing.
now comes the part you need.
right now if you did the above, the new tracks created, are routed to the master track,
all routed to 2 channel - stereo
but you want more than that.
so you do these steps, for each of the created tracks.
1. click the routing button
2. clear the checkbox on the top left (master/parent send).
3. increase the number of audio channels of the track (you can have up to 64 per track)
4. now in that window, you have Audio hardware Output.
5. you add a new hardware output
6. now you can click on the new output and choose different channel.
instead of 1/2 you might choose 3/4
and so on.
hope helped you with my broken english