If you're getting the "MIDI Driver installed properly but in use by another program..." error, there's an easy fix... If you download the Loopbe1 driver from nerds.de, you can use that as your MIDI output driver. Just make sure you have your DXi synth turned on, or you won't get any MIDI sound.

You don't actually want to use the driver itself, it just gives you something to select other than the Wavetable... works every time.

http://nerds.de/en/download.html