The new M4 + DSP amplifier can be seen as the little brother of the M6v2 model, as it comes with the same DSP technology and features. The only difference is that the M4 + only has four amplified speakers, but offers more power per channel than the larger M6V2. Both models also share the very compact housing dimensions, made possible by the ingeniously constructed 4-fold laminated circuit board.
Review from German Car & HiFi 
Link: https://musway.de/assets/m4plus-ch.pdf