Attach the audio outputs of the MIDI hardware synthesizers to your computer's sound card. Use audio cables compatible with both the synthesizers and the sound card. A professional sound card usually will have quarter-inch connectors, as will the synthesizers. Cables with quarter-inch plugs on both ends will suffice. Alternatively, use cables with the connectors that work for your equipment.
Create a new audio track in Sonar. Choose "Track" and then "New Audio Track."
Assign the inputs for the new audio track to the inputs of your sound card.
Arm the audio track for recording by pressing the "R" toggle switch on the track.
Press the "Record" button on the Sonar transport bar.
Press the "Play" button; the project will begin recording. The MIDI data sent by Sonar to your synthesizer comes back into the application as audio data.
Choose "Edit" in Sonar, then click "Select All."
Click "File," then choose "Export Audio."
Select "Tracks" in the "Source Category" drop-down menu.
Choose a location for the final audio conversion of the MIDI tracks. Use the "Look in" drop-down menu. Type in a file name base in the "File Name" field. Each track will use this file name as part of the naming convention.
Click "Export." All of the MIDI tracks are converted as individual audio tracks and saved in the location you specified.