Miden,

Even if you Midi the MM6 to an S90ES you're still going to be dealing with 32 note poly. The S90ES will just be a controller thus turning the MM6 into the tone generator.
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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.