Why does the church of Christ forbid the use of instrumental music when it was commanded in the Old Testament?

I believe the first principle that must be examined in answering this question is where do we go for authority in religious matters today? God’s plan for saving man and instructing the church today is found in the New Testament. 

Jesus came to do the will of God, and in so doing took away the first covenant that He might establish the second (Hebrews 10:9). The new covenant is better than the first, being established upon better promises (Hebrews 8:6).
When Jesus died on the cross, he took away the old law of Moses, making it of none effect (Ephesians 2:13-16; Colossians 2:14). He replaced a faulty will
(Hebrews 8:7-9) with a new one (Hebrews 8:10-13). Though the Old Testament is given for our learning (Romans 15:4), we cannot appeal to it for justification for anything we do in the worship or work of the church (Galations 5:1-4). 
In Romans 7:1-4, Paul described the Mosaic Law as a dead husband. What he meant in his illustration is this–one must be married to Christ to be a part of the bride of Christ, the church. The Israelites had formerly been bound (as a bride) to the Mosaic Law. But Paul said they had become dead to the law by the body of Christ (the church, Colossians 1:18), that they might be married (bound) to another, even to him who is raised from the dead (Jesus).
So, while Psalm 150 (and other Psalms) do command the use of instrumental music in praise, the question remains, are the Psalms an authoritative body of work to guide the church today. In this respect, we must answer in the negative.
A point of interest, there are a host of other commandments in the Old Testament that men have no intent on following today, for example, the laws of capital punishment. God’s people were commanded to put to death a wide variety of law-breakers, including: adulterers (Leviticus 20:10), homosexuals (Leviticus 20:13), children blatantly disobedient to parents (Leviticus 20:9), sabbath breakers 
(Numbers 15:32-36), failure to observe the Passover (Numbers 9:13), etc. Why is there no appeal to observe these parts of the law?

Incidentally, unlike the examples provided above, instrumental music was not a part of the Law of Moses. The introduction of instruments came hundreds of years later at the hand of David. In fact, the instruments are attributed directly to David in several passages (1 Chronicles 23:5; 2 Chronicles 7:6; 2 Chronicles 29:26).

Finally, in Amos 6, the Lord pronounces a curse upon those of Israel and Judah who are “at ease in Zion” (6:1), and in connection with this condemns those who “invent for yourselves musical instruments like David” (6:5). This leads one to believe the Lord was not altogether pleased with David’s addition, for why would God use a proper course of action to illustrate a bad example?