know I'm getting a signal because the meter is registering on the track
That doesn't mean anything, as it depends how you inserted Session Drummer. If you only have a MIDI track and no audio track to output the audio, then that is your problem. MIDI is just data and the MIDI track needs an audio track to make sounds.
I'm 99% sure that all this is a routing issue. But no screen shot is necessary, as you just need to click insert, selecting the soft and then select MIDI Source and All synths MONO
or Stereo outs and synth property page track and Sonar routs everything for you. Its easy cheasy bro.
If its not the routing then its a sound card driver issue that you need to correct yourself by adjusting the ASIO or WDM settings, but im almost sure its a routing issue
CJ