I second the Focusrite interface. It will be the soundcard you need. Most are now connected via USB.

You can get one that incorporates midi into it or simply get a plain audio interface. Mostly that will depend on the kind of midi plug on the Ketron SD2. See the pics of the backside of the one Floyd linked for you. Older midi gear uses the 5 pin din plug. Newer stuff uses a USB connection to the computer.... either will work fine with routing the audio from the midi to the monitor speakers on the Focusrite.


You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.