At the top of the Ezdrummer window, look for the mixer. Select all channels, right click and select "multi out".
At the top of the window for the VST interface, you have inputs and output. (They look like two arrows). The right arrow is your input (atom pad, keyboard etc). The left arrow is the outputs. Click this and a drop down menu opens with check boxes, with the first one selected as "EZ1". Tick all the boxes and close the menu. You should have the same number of channels available. They'll be labelled "Ez1,ez2, Ez3".