Let see the picture below to understand the midi window. This is all the Midi parameter for each channel Bexpand use. 

Midi window.

The Midi parameter you see is for the channel currently selected. Select another channel to see its parameters.The current instrument for the channel can be changed by program change message exept if you set the Freeze flags. Program message number map the instrument number.

Midi parameter like main volume or panning can be set in real-time by Midi message or can be fix in the software. You can assign for each Midi parameter a Midi message. For example, you can fix the main volume of the current channel with a Pitch Midi message.