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This has been discussed here over and over.
I'm still happy that Helix is such a professional gear that only has stable and reliant connections.
Otherwise I had sold it ;-)
Not via MIDI. But I guess you can use either the AUX-In or Mic-In inputs to use the Tyros DSP-effects. Check the Tyros manual:
Tyros 5 manual
Guitar via DSP
...interesting...
You're reporting for half a year of a guitar that your friend bought...
Maybe it's time to make it a little more concrete, for example with a recording of the problem - otherwise it's hard to judge over it ;-)
I'm sorry that you can't be helped with your instrument!
However, this says little about other JTVs and certainly nothing about Helix.
Good luck again, cheers!