First, let me answer your point about songbooks. There is a difference between an expedient or aid, and addition to a command. Songbooks do not add or change the command to sing. They only aid in the singing. However, if mechanical instruments are used in worship, then that is adding to the command to sing. It is a different type of music.
As I have said before, while the Old Law is not binding on Christians, the Old Testament was "written for our learning" (Romans 15:4). There are numerous examples in the Old Testament (Cain and Abel, Nadab and Abihu for example) where people took it upon themselves to do something not specifically forbidden by God. Cain's offering was not accepted by God, and Nadab and Abihu were destroyed by God for offering something that was different from what was specifically commanded. When a specific command was given in these cases, doing something outside of that specific command was not authorized.
Again, "Says You." Why is is that musical instruments are singled out? Where is the Biblical basis for your distinction between "an expedient or aid" and "an addition to a command"? Why are songbooks one, and instruments the other?
It's apparent to me that you are doing your best to find a rational explanation and scriptural defense for something you learned as a tradition. Don't worry about it; it's something most serious Christians experience at least once in their lives. With regard to the issue of instrumental music in church, your perspective plainly makes sense to you, and it does no harm to the Gospel for you to worship without instrumental music. However, to state generally that instruments are forbidden in Christian music is to overstep your Biblical authority, and to cause your brothers and sisters in this very public forum to stumble. Let's not, all right?
All right...if that's the standard...then you would say that when a specific command is issued by God to individuals, that those individuals should follow that command explicitly, neither adding nor omitting anything.
Is that an accurate assessment of your point of view?