Where will the slideshows be used? Online? At seminars? What will they play back over?

I would leave the voiceover iself to be handled by ducking if possible, so that shouldn't be too much of a concern.
Background music is just that; background. Don't try to bring out the bass, or cymbals, or anything that may distract from the voiceover, the idea is to have the music there, but not have the user notice it.


I do not work here, but the benefits are still awesome
Make your sound your own!