I went down that path before but the gap between AK120 and HM901 is so big that I end up still taking out the HM901 ALL the times. I finally sold the AK120 for a dx50 as my "occassional road use" and for emergency situation DAP (read: forgot to charge my 901)..... and even I had now got the 240, with new toy syndrome and whatnot, I m STILL listening to 901+mb+re600 right now as I'm posting this....
I know what you mean. Actually I thought about getting a DX50 or X5 for occasional use too, but since the price of a second hand AK120 isn't out of my reach, and it's still smaller and easier to handle than a DX50 or X5, w/ less issues too, I couldn't help but went for one. I think I'm done w/ portable DAPs for now.
Tried AK240 yesterday, side by side w/ AK120 for nearly an hour with same songs in both, I still prefer AK120's smaller size and slightly warmer tone.