Is the "echo input" button on the MIDI track blue? Is the output for that track (or its corresponding audio track which should be set with your MIDI track as the input) set to a bus (preferably the Master bus)? Is the Master bus' output set to your sound cards' monitor output? If "No" is the answer to any of the above, change the output accordingly.
About the latency issue and the "gs wavetable," are you referring to the Windows Audio output/input or is that a setting in SONAR's audio preferences? Where do you find the "gs wavetable" setting, in Playback Timing Master? Also, how are you disabling your internal sound card, through the device manager?
Although the above is rudimentary, sometimes we forget a detail or two. Please let us know if you need additional help if the above does not apply.
Kind regards,
tecknot