Use the Mk3 and Mk4 anywhere: Speakers, components, Power Supplies.They can help to take a touch of hardness out of a system.
Black Diamond makes two versions of the cones, Mk 3 and Mk 4, which have different sonic signatures. Although they vary by sonic characteristics (the Mk 3 is warmer, with more midrange bloom while the Mk 4 is more linear in response), your system may sound best with a combination of both types.