A Japanese person, teaching a college course on musical composition, described it, in terms of the five, philosophical elements.
He said that it would be monotonous and incomplete, unless it had the qualities of fire, water, earth, etc.
Maybe, this is an explanation, for how deaf people were able to write symphonies, assuming that they were somewhat mathematical, and that sensations can be experienced, through different organs.
I believe it would be interesting, if these images were compared, to see whether synesthetes are experiencing the same numbers and tones, in a similar way.
One simplistic way of doing this, would be a multiple choice test or online poll (if there are not too many of those, already.)