I think you may have hit it, Doc, the KJB translators were very familiar with Jewish custom. Just look at these concerning "pslams, hymns, and spiritual songs":
5568 qalmov psalmos psal-mos’
from 5567; TDNT-8:489,1225; n m
AV-psalm 5, Psalm 2; 7
1) a striking, twanging
1a) of a striking the chords of a musical instrument
1b) of a pious song, a psalm
5215 umnov humnos hoom’-nos
apparently from a simpler (obsolete) form of hudeo (to celebrate, probably akin to 103, cf 5567); TDNT-8:489,1225; n m
AV-hymn 2; 2
1) a song in tithe praise of gods, heroes, conquerors
2) a sacred song, hymn
4152 pneumatikov pneumatikos pnyoo-mat-ik-os’
from 4151; TDNT-6:332,876; adj
AV-spiritual 26; 26
1) relating to the human spirit, or rational soul, as part of the man which is akin to God and serves as his instrument or organ
1a) that which possesses the nature of the rational soul
2) belonging to a spirit, or a being higher than man but inferior to God
3) belonging to the Divine Spirit
3a) of God the Holy Spirit
3b) one who is filled with and governed by the Spirit of God
4) pertaining to the wind or breath; windy, exposed to the wind, blowing (In conjunction with "songs" if the Greek "enthusaist" will allow, KJB translators did.)
The we have this: (making melody)
5567 qallw psallo psal’-lo
probably strengthened from psao (to rub or touch the surface, cf 5597); TDNT-8:489,1225; v
AV-sing 3, sing psalms 1, make melody 1; 5
1) to pluck off, pull out
2) to cause to vibrate by touching, to twang
2a) to touch or strike the chord, to twang the strings of a musical instrument so that they gently vibrate
2b) to play on a stringed instrument, to play, the harp, etc.
2c) to sing to the music of the harp
2d) in the NT to sing a hymn, to celebrate the praises of God in song
Though it's NOT my intention, and I do love acapello, this would change the view of the Primitive baptist on their objection to musical instruments used for worship.
Nearly all the Pslams are "to the musician". Hymns are sung "acapello", the " Church Hymnal" is full of Hymns and Pslams and Spiritual songs for the purpose of making melody in our hearts. And Yes , I know it's a Co G hymnal, but it has many of the "baptist" songs in it.