Piano and live electronics

I'm not an expert, but I would think you'd want some sort of directional mic to help cut down on the extraneous sound you have to contend with. I know my dynamic mic is somewhat directional.

If I understand you right, I think I've done this sort of segmenting inside of Ableton. I used filters to remove the sound outside of the range I wanted it to apply to, combined with gates and such to trigger the effects to run. There was a difficulty though, because when I was playing a low octave for example, and it triggered the low octave effects, I ended up wanting the effects applied to the whole spectrum, because otherwise it sounded weird with the overtones filtered out.

So, I think you might need two lanes, one of those lanes will be warped in whatever way you need to handle the controls, then the other lane will be the sound that will actually be controlled (not sure if you want the piano sound itself). Maybe checkout fiddle~. I believe you could use it for the control lane to detect the pitches, though I just found it recently so I'm not sure if it'll be accurate enough on it's own or if you'll need to manipulate the control lane sound in preparation using filters etc. in MSP. But, I believe this will give you midi note data, which seems to be ideal for segmenting the key range into zones.

You may even be able to get away without multiple mics, since you can just filter the frequency range anyway in the control lane.