The Midi synth appears to be gone from Melodyne 4.
If this is true, how can you work with the "Audio to Midi" process in polyphonic mode
  to match the midi notes to the audio ones you want to keep and export to midi?
 
In short, where is the Melodyne midi synth located?
 
SOLVED: They moved it to a different window.

I just drag a polyphonic audio track to a blank MIDI track and Melodyne 4 converts the audio to MIDI.
 
I have never done that conversion in Melodyne but YMMV.