Ok, this is one aspect that I mentioning several times in the ST thread. This is about the reproduction of cymbals (and also of snare drums), and this is why I mentioning before in this thread that, in my opinion, the high frequencies are the more difficult frequencies doing correctly in a headphone. With the 12 (and 5909) you having a more big soundstage and the perception of more details (this is with the help of more treble presence), but for actual realism of cymbals and snare drums, the ST clearly is more accurate, in my view. This is similar like when in photography some photos showing more details or more contrast in colours, but ultimately isn't so real like what your eyes perceiving in reality -- more impressive initially, yes, but not so natural at the end.
But I must insisting that the io-12 is really a very, very good headphone with really very good sound. And, if I don't know the ST, I keeping definitely. I still need doing more testing for being 100% sure that I keeping the ST and not the 12, but right now I'm 85% the ST is my preference.