I never do soundboards, but they should work unless the MicroTrack can't handle a soundboard feed without some sort of attenuator. Hopefully someone else can chime in on this.
If nobody confirms that it will work, try starting with the the L/M/H switch set to L and the levels as low as you can set them. If the meters still go over 0 DB & the clip indicators are lighting up, you need an attenuator. If they aren't going over, you can increase the gain as appropriate.