Maybe Higayon is an instrument. However, we know it means thoughts or expressions, as in hegyon libi. Alei higayon bkinor seems to make sense as expressing oneself through the music of the kinor. Otherwise why lump together two separate instruments? And wouldn’t it be Alei higayon vkinor (a vav not a beis).
As far as the high point, I mean in the sense that this is part of the kedusha which the entire kahal says together out loud.