Let's take the common standard that A = 440. You might ask "440 what?" The answer is 440 hz. Each note we play corresponds to a specific number of hertz, which is the number of full-period cycles that the sound wave makes in one second.
Why is this bit of mathematics relevant to a historical/theological SE site? Well, to ask whether music existed before the Earth, one must ask: "What is music?" so that we know for what it is we are searching. That being said, we can say for certain: part of what we call music is mathematical in nature.
Indeed, not only does each note have a specific frequency, composition of musical pieces is accomplished through varying patterns of repetition. Each note in a scale is a certain frequency above the last note in the same scale. You can play (theoretically) any scale or pattern in any key. To play a song or scale in a different key simply means that we adjust the starting frequency of our scale to another number of hz, and then we play the notes of the scale with the same offsets they had in the first key. We can listen to the same scale played in different keys and recognize their "ontological" (as you put it) structures as being distinct (after all, they may never share a frequency between any two notes in the entirety of the two scales) while their relative mappings from a given frequency to next frequency remain the same.
Let's assume for a second that light can be converted from its ontological structure into a mechanical form that we call sound. Let's assume that at least in theory it's also possible to go the other way, from sound to light. What this means in effect is that we could "transpose" Martin Luther's "A Mighty Fortress is Our God" into a different key: one whose starting "note" exists in terms of light and not sound. Our song would be "played" by altering the frequency of the light, according to our transposed score, that is emitted from our source just as is done in the mechanical world of guitars and pianos.
So from this perspective, this is a relatively simple question to answer: ontologically, music is sound, or at least some specified forms of variation on an energy wave through a certain medium. There must be mediums through which to source and send the variations. This means (in our standard definitions) that ontologically, music did not exist before there was anything by which we could reveal a score.
Now, there's a different question, which is the one I think you are meaning to ask. Ontology aside, could the principles of music have existed before the creation of the Universe? After all, the principles of music can be applied in many places.
In information theory, we consider the "quantification of information" (phrase is ruthlessly stolen from wikipedia). What is information? Information is "a sequence of symbols that can be interpreted as a message." As such, we can quantify (extract and/or extrapolate meaning from) it. If we had time, ability, and desire, we could analyze all symbols in the universe (think beyond molecules: for instance, why could you not apply the principles of music to compose a piece written in the medium of "time?" Perhaps in this medium A = 440 nanoseconds). Martin Luther's famous hymn might (and probably does) actually exist in several places if we could apply the correct techniques to extract it and the creativity to look for it.
So from a logical perspective, one need only have information and the ability to quantify the information in order for the principles of music to exist. From a philosophical perspective, there is no definitive answer regarding the question as to whether or not the principles of music exist if either or or both of information and a quantifier are absent.
From the Christian point of view, the philosophical question is meaningless. God always was and is. The quantifier has always been present. In order for God to "think," this must also mean that symbols have always been present, as mathematically speaking thinking is the processing of symbols. Even though the symbols God processes originate from Himself, they are present nonetheless or He would have nothing on which to act. He would be insentient.
This demonstrates that in whatever medium God chooses to operate, the principles of music have always existed.
Minor nitpick of the question. It's a good topic in general but it's sort of all over the map and ends with the too-broad question about denominational views on music. I've interpreted it as "could music have existed ontologically before creation?" I can understand how others would have an urge to answer a different question.