Everything I have read about systhesis so far tells me that all people can have the experience but only some do.The brain of most of us just does not allow it to happen.
I feel that if a person really worked at it they would see colors and feel something different in music.I may be wrong but that is what I think.
I am not even sure if I have systhesis because it never happened to me before about a year ago.According to what I have read about it most experience this at a young age.It could be that my brain chemistry has changed somewhat due to medications I take as well.I am not sure.I am just glad it happened to me.