I guess my question then would be, how did the Jews of old worship God when they gathered together at the Temple... Admittedly, I know very little about Jewish worship.
Psalm 150:3-5 says, "Praise him with the sounding of the trumpet, praise him with the harp and lyre, praise him with timbrel and dancing and pipe, praise him with the clash of cymbals, praise him with resounding cymbals." So clearly instruments were permitted, even encouraged, in Old Testament times.
However, the argument against instruments stems from the understanding that the New Testament, in introducing a new covenant, does not speak of using instruments. Personally if the Bible doesn't speak against it, or any other issue, then I think that means it's ok, so long as it fits with other Biblical direction, that is, that it is God-honouring, and loving towards your neighbour (but then, if it were contradictory to these, that would be speaking against it, wouldn't it?). However this question was likely raised by someone who is of the persuasion that God instructs, and if He has not specifically done so, it should be avoided. A sound principle, which I won't hazard to argue against, though I will say on this issue it is rather non-applicable.
Here's why: this question is built upon the assumption that music is how worship is achieved. Consider Romans 12:1, "I appeal to you therefore, brothers, by the mercies of God, to present your bodies as a living sacrifice, holy and acceptable to God, which is your spiritual worship." Worship is anything you do in this life for the glory of God. Presenting yourself as a living sacrifice is a metaphorical representation of how we commit our lives to God; we give up our bodily desires FOR God. So in any circumstance we do something that is not for man's own glory, we are worshipping God. So titheing is worship. Giving to Opportunity shops is worship. Prayer is worship. Reading the Bible is worship. Any time we demonstrate submission to God, we are worshipping Him. We can sing to God in worship, we can play instruments to God in worship. If we do these things in reverance. So music is most certainly something that CAN be used for worship, but it is not what worship is. Worship occurs within the heart, and whether you use an instrument to express that heart state seems irrelevant to me.
Music is also a great means of evangelism (which is commanded unto us in the Great Commission in Matthew 28) as it speaks to a culture, it's engaging, and is scientifically demonstrated to be the only activity which stimulates every area of the brain, hence why it can both provoke and express such strong emotional reactions. So to be able to harnass that for God is truly extraordinary.
Basically, what this issue comes down to is the heart behind it, as it is with everything we do on this Earth.