I believe you as I have read more than a few guys mention the harsh highs on the IM03. On my pair however I have never heard it ever. It is musical smooth full bodied sound and has solid control in the highs. If anything compared to my DN2000Js the highs are somewhat reserved. With the stock cable the IM03 sound a bit warm in tonality as my pair the highs take a step back in the balance a touch. Upgraded cable tightens the bass end but also brings out more detail balancing out the sound and neutralizing the tonality. It sounds world class with this combo.
I did forget to mention. My pair went through a rigorous burn in period and I only use wide bore JVC spiral dot tips. One issue with AT earphones is they are guilty of using stock in house silicones that don't necessarily give the best sonics to their earphones. If you guys are serious about opening the sound of your earphones get yourself a box of spiral dot tips and try them out with any earphone you own.
I let a good friend of mine borrow my earphones and lets just say I trust this guys hearing more than anyone else here on the threads. He had nothing but praise for them as well. This guy hates harsh highs. I know there are different variables on exactly how we all hear things but harsh highs and sibilance is just that. My IM03 is the opposite of this.
The highs on my pair are smooth clear and extended but never once have I ever heard sibilance on them.
Thanks for the tip regarding the JVC Spiral Dots. I'll be sure to ask to try the IM03 with them again in future. In my experiences, the IM03s that I've auditioned were all relatively burned-in pairs, with stock cables and stock tips.
It's a shame that I found the highs on the IM03 a little too strident; I love its otherwise energetic but clear sound. Nevertheless, I defer to your judgement, and I'll be inclined to give them a lengthy audition in the future.
Cheers!