It is only in vst version of EZd. Top right hand corner of EZdrummer interface is "Menu" drop down. It is next to the orange section where you choose your kits/EZX.
Click on menu, 8th item down is "Sonar Options". Choose "Show number of outputs on startup".
Then close the project. When you then re-open the project you will be asked to choose number of outputs,, choose "8 Outputs", and all is well.
I don't have EXd do this all the time, only when I open a project that I started with EZd1.
HTH