The MM-6 really isn't a new concept for Yamaha at all. They've already done something like this and is sold "big time". The MM-6 is a essentially what the original DJX was with some improvements.
Just because some of the patterns are just drum and bass, doesn't make it any less of an arranger as the S-500. They're both arranger, but each has a different platform. It's good that some of the patterns are just drum and bass. This allows the player to utilize the arranger function, but also keeps the style simple enough so that the player can do more and not be locked in to a the style itself.
You have to have owned or spent a good deal of time with the original DJX to see my point. I owned the original DJX. That board was way ahead of any arranger for modern music, and even today it's styles would still give current arrangers a good run for their money. Yamaha shot themselves in the head (not in the foot), but the head when they released the DJXII. The things they did and and left off on that unit was not taken well by consumers.
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.