The track icons are very limited, especially for music which is not rock, pop and classic. So the best solution would be a small track icon editor, where you can load an image which is rendered down to te right pixel size or/and you can edit your track icon. This editor could be very limited. Just two colors: black and white, with different oppacitites(for grey tones) and brush sizes.
Inside the macro shortcuts you can load pictures, so like that but with the basic editor.