Hmmm... having been let down very badly by my Cowon J3 with anything other than basic dynamic IEMs (the J3 sounds good in itself but lacks sufficient grunt to properly drive low-impedance CIEMs), I wouldn't even consider buying another DAP (finances notwithstanding) until I know for sure that it has:
1) low output impedance
2) good current delivery
Far too many people get sidetracked by glitzy techno-features or what DAC the DAP utilises. The amp section is absolutely every bit as important!
(please spare me any recommendations to 'add a portable amp' - I wouldn't buy a ferrari and then 'add an engine').
I had to sell my iBasso DX100 to free-up some cash, but that is one damned good DAP, even though it is unfortunately a bit on the bulky side. The DX100 really drives CIEMs properly and the difference in sound quality is moderately-spectacular!
I'll watch the AK100 with interest, as with the HM-901, but it's all talk until we get some proper reviews as to whether the amp sections of these DAPs are designed to do their job properly or if they're just window dressing.
I'm curious per your experience w/ the Cowon J3 and sensitive IEMs. I am pondering the purchase of a Cowon J3 hoping it will mate w/ my Shure SE535 properly.