Consider one interpretation tool in the book of Revelation:
Rev 1:13 And in the midst of the seven candlesticks one like unto the Son of man, clothed with a garment down to the foot, and girt about the paps with a golden girdle...16 And he had in his right hand seven stars: and out of his mouth went a sharp two-edged sword: and his countenance was as the sun shineth in his strength.
1:20 The mystery of the seven stars which thou sawest in my right hand, and the seven golden candlesticks. The seven stars ARE the angels of the seven churches: and the seven candlesticks which thou sawest ARE the seven churches.
So you understand that there are pictures in Revelation that mean spiritual things. Then look at the use of instruments in Revelation:
Rev 5:8 And when he had taken the book, the four beasts and four and twenty elders fell down before the Lamb, having every one of them harps, and golden vials full of odours, WHICH ARE the prayers of saints.
Rev 14:1 Then I looked, and behold, the Lamb was standing on Mount Zion, and with Him one hundred and forty-four thousand, having His name and the name of His Father written on their foreheads. 2 And I heard a voice from heaven, like the sound of many waters and like the sound of loud thunder, and the voice which I heard was like the sound of harpists playing on their harps. 3 And they *sang a new song before the throne and before the four living creatures and the elders;
The Biblical Response:
(1) they aren't literally playing instruments. Just like Jesus is not literally holding the seven stars. And (2) instead of looking at the present age issue (because it seems that this is going on in Heaven while historical events are taking place on Earth) I would ask if they are singing an inspired song given be God for them to praise Him with. If so, then they are exclusively singing a Psalm. When I get to Heaven, I'll sing it with them.