I don't get it. If the ES5 is more transparent, more realistic (from your description of cymbals and horns), shouldn't it be the best audio monitoring tool, despite the IERM having been designed specifically with that purpose in mind?
Not necessarily. Remember, when monitoring studio music you want to make out finer details. Sometimes this means touching up the treble a bit, leaning out the low end, etc. You want uber clarity yes, but transparency, as in getting 'lost' in your music, is not necessary or even desired for a professional mixing tool. I'm notorious for bad car analogies so here is another one. Imagine you want to buy the 'best' car. Another person says, check out this new Ferrari. It has the best 0-60, best skidpad performance and best braking. So you go for a test drive and you realize you can't carry your luggage and golf clubs, it only seats two, gets terrible mileage and hurts your back getting in and out. The Ferrari is the 'best' car as a 'tool' for a specific purpose. To live with as a daily driver is another matter. YMMV, no pun intended. Hope that makes some sense.
Btw, thanks for all the positive feedback guys. Appreciate it.