How are the tracks set up? Did you use a simple instrument track? A separate audio and midi track?
The basic idea is that you want the input to the audio track (or the audio portion of the simple instrument track) to pick up the output from the Primary Output: Stereo from Dim Pro.
You should just have to change the audio routing assignment for the track to pick up stereo output from Dim Pro, and your midi playback will then sound in stereo.
Bob Bone