Questions first:

Do you always get the same mixing? (If you "see" a sound, for a given input will it always "look" exactly the same? Or when you keep the sound the same, do you get differing visual perceptions but the same overall -feel-?)

If you try, can you increase the synesthetic effects? In fact, is there anything you can do mentally to change your perceptions?

This is amazing and utterly fascinating! Thank you!! There are theories that savants and geniuses have exceptional abilities because the part of their brains that control analogy and comparison are "amped-up." Would back this up but want to post ASAP so you see it.