The MIDI to VOICE parameters (M>VOICE) in the HRM effect (HRM1–3, Page 5) are only displayed when a MIDI device is connected to the VE-500's MIDI IN connector via a 5-pin MIDI cable. If Page 5 does not appear in the HRM effect settings, check that a MIDI cable is connected to the MIDI IN connector.
For details on M>VOICE parameters, refer to "HARMONY/VOCODER" in the VE-500 Parameter Guide.