the ES100 can drive my ATH R70X headphone easily, so it is a very capable amp dac. i don't think any iems would pose a problem for the ES100. other DAC aside the ES100 to consider is the Fiio BTR3. it has a "snappier" attack to the sound, while the ES100 has a more pleasant and natural sound. both are equally great product.
although the JVC and M0 combo are easily doubles the price of the M2 or the TW

interesting that you put the M2 and the TW on the same rating on sound, as i really like the sound of the M2. how about the whole package experience (the feature, battery life, convenience, etc) between them both? which one do like more?
I might be parroting about this a bit too much lately, but i really recommend the Sabbat X12pro. it's like the KSC75/portapro in a really small size, with great 7 hours battery life, and small charging case size.
I'm curious how this compares to the Bose soundsport, as they have the similar open sound