Bruce, first let me say welcome to the forum. We would be honored if you would hang around and participate with us.
You are right. "Psallo" is used without modification in the other verses. And yes, "psallo" meant, among other things in the OT, "to pluck". However, by NT times, the large majority of reputable scholars agree that the verb simply means "to sing". If the Scriptures meant to "sing and play a mechanical instrument" one would expect to see the instrument expressed in at least one of the verses.
AJ inadvertently brings up a good example. In Ps. 150, OT believers were commanded to sing and play the harp, cymbals, etc. So where are those like verses in the NT that state such things?
None of the scriptures dealing with music in the NT infer or state an instrument is to be used except for one. That Scripture is Eph. 5:19, and it states the instrument to be used is singing with the accompaniment of the human heart. The heart is the instrument. If Eph. 5:19 states as such and the other Scriptures are silent on the matter it is reasonable to assume that it applies to them too in absence of contrary evidence. (Particularly with supporting historical evidence.) So I guess in a sense, we do have "instrumental music". The instrument is just spiritual instead of physical.
So how do we know "psallo" means to "sing" by NT times? The word of some scholar? Probably the best witnesses of the fact is the early NT Christians themselves. There is a thread somewhere on this board with some Early Christian references as to how the earliest Christians interpreted these verses and how they worshipped.
(AJ, the Orthodox Church still worships and teaches this today. You might check out what the historical sources say on the subject. I know this carries some weight with you.) We still sing Psalms today, too. They don't have to be accompanied by musical instruments to be sung, and apparently weren't until the 6th-7th century in the Church.
So in short, "psallos" does not authorize musical accompaniment in the NT because....
1. The Greek language lexicons show a different NT time use.
2. Every Bible translator translates it "sing". I have never seen the verses mentioned ever translated "sing and play". Ever.
3. Historical sources up until the 7th century disapproved of it and thought it contrary to the Word and the Apostles' teaching. It is a modern invention in the Church.
BTW, I also have never heard anyone actually claim that we HAVE TO use instruments based on the "sing and play" argument, so I think even those who might wish to use them think it would be weak to stand on that alone.
The best case I could see for IM would be one of "christian liberty". However, to me, an extremely strong case can be made for non-IM based on
1. authorization
2. historical evidence
3. expediency
Each reinforces the other and makes the case that much stronger.
Probably more than you wanted to see or read. Take what is useful to you. In any event, again, welcome to the forum.