Question Can I get harmonies on my guitar if I plug it into the instrument input

No, the instrument input is not designed to produce harmonies for instruments. In order to produce harmony the microphone input must be used.  Although all TC Helicon products are designed with the human voice in mind, we have quite a few customers using them successful with other sources like fiddle and brass instruments.
This answer applies to the following products:
  • VoiceTone Harmony-G XT
  • VoiceLive 2 / VoiceLive 2 Extreme Ed.
  • VoiceLive Touch
  • VoiceWorks
  • Quintet (discontinued)
  • VoiceCraft (discontinued)
  • VoiceLive (discontinued)
  • VoicePrism (discontinued)
  • VoicePrismPlus (discontinued)
  • VoicePro (discontinued)