I know that all these varies on their DAC chip and their implementation. But after reading eke's thread about the various DAPs, I think the overall consensus is that while there are differences, it is quite small and we are splitting hairs.
So i 'm going to just focus on the amp section. Currently I'm rocking a set of GR07 MKII, and a UM Merlin straight out of my phone after my previous Creative DAP died on me. So I'm in the market for a new DAP. As much as possible, I will like to avoid carrying a brick out with me. The DX 50/90 form factor is just about the biggest I will go.
Based on the 4 DAPs I listed, are they sufficient to bring out the details in my two IEMs? I don't for see myself getting portable or full size cans in the near future since the shape of my head/ears makes it a pain to wear even with ultra padded pads.
The idea I'm floating now is that if all four are equally competent at driving IEMs, I'll go with the cheaper option of X3 or DX50. Especially now that their respective upgrades are in the market, both of them can be found for cheap.
Perhaps someone can just rattle off something about each player's amp section, I can then make an informed choice.