Create box, bar, tube etc. sub-types of zither and move everything to the correct subtype.
this is also related to INST-679 so therefore also INST-392

https://en.wikipedia.org/wiki/List_of_musical_instruments_by_Hornbostel%E2%80%93Sachs_number:_311.222
https://en.wikipedia.org/wiki/List_of_musical_instruments_by_Hornbostel%E2%80%93Sachs_number:_31
https://en.wikipedia.org/wiki/Hornbostel%E2%80%93Sachs#Tube_zithers_(312)
https://en.wikipedia.org/wiki/List_of_chordophones_by_Hornbostel%E2%80%93Sachs_number#Tube_zithers_(312)

http://www.rudravina.com/html_gb/inst_01.html mentions that tube zithers are a later development of the stick zither.

this site also has a great index of terms: http://www.rudravina.com/html_gb/divr_01.html#t
"Tube-zither: A (plucked or bowed) musical instrument whose strings are stretched all the way along its resonator which is made of a wooden tube."