In Sonar it’s best to open EzDrummer via the Synth rack. This will set up your ‘ins’ and ‘outs’ automatically. Synth rack has options accessed through an options dialogue box in Synth rack. You need to check the ‘midi source’ box and you get one track of midi (it’s all you need for the midi part). Now you need to set up the audio/synth track(s). You can have the EzDrummer kit all going through one audio track by checking ‘first synth audio output’ or you can have different parts of the kit going through their own channel by checking ‘all synth audio outputs (stereo)’. If you choose this second option (you will once familiar with it) it will automatically create 8 audio tracks – then you need to alter the ‘mixer’ in EzDrummer to ‘multichannel’  –  you just go the EzDrummer mixer and where it says ‘output’ it has to the right ‘TRK1’ – right click and check ‘multichannel’ – and your kit will automatically go to the different audio tracks you set up. EzDrummer defaults to 7 tracks.

One midi track holds all your midi data, which you can edit and alter but this has no sound and that’s why you have an audio/synth track(s) in order to hear the sounds. These audio tracks can have effects etc applied to them.

In Sonar, Edit>Select>All
Then
File>Export>Audio
You can select a location where you want the audio file to be saved, as well as the bit depth and sampling rate. Sonar converts your drum tracks  and other MIDI tracks to audio on mixdown.
 
You can select By Time if you want to (to convert just part of the tune to audio) and you can mute tracks during mixdown too if you want.