Using one channel of an amplifier to drive each Ribbon and midbass so that a stereo pair of speakers requires 4 channels of amplification. Means that instead of driving a speaker full-range with a single channel of amplification, through a single set of speaker cables, you actually connect two sets of cables, with each set driven by a separate amplifier, or separate channels of a multi-channel amplifier. This way, low frequencies and high frequencies each receive dedicated amplifiers.