I still don't see the logic in them not having midi jacks on the S-500, but having them on the MM6 though. These are both arrangers (while one may not have the full style sections.., it's still an auto accomp keyboard), but Yamaha at least gave the MM6 midi jacks... How about this for a missing basic feature. Yamaha claims the MM6 to be a "synth" yet the MM6 is missing ONE very important feature found on a synth.. The MM6 has NO PORTAMENTO!!!!

I had considered the MM6 just for some cheap Motif sounds, a bang around board, and so on, but when I found out it had no portamento, and even it's onboard midi was limited--I said the hell with that and bought the Motif ES6 (before they were all sold out).
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.