My MIDI tracks aren't loud enough in relation to my audio tracks!
In Mixcraft, click on the "Change Instrument" option to the left of your MIDI track. Next, click on "Show Details," and type in a higher value for the volume setting. For example, you could change the default "100%" to "200." Now play the track and see how it sounds.
Of course, in addition to changing that setting, you can also turn up the volume slider to the left of the track for added volume.