Marathon Professional Digital Echo reverb Karaoke Mixer Processor. Marathon MFX-100 Digital Echo and Reverb. Features 3 microphone inputs, 99 digital reverb and echo presets, and is tailor made for the Karaoke DJ. Its straightforward design makes the MFX-100 easy to operate and features that include separate microphone level controls, and crossover adjustable sub-woofer output make it well suited for professional karaoke applications.