I have a similar experience after doing a half hour audition with my buddy's DX100.
Was intending to buy the DX100 thinking that it will be better than my HM-801. As usual gadget person's bad habit, thinking that new gadget should always be better than old one.
Tested same songs with DX100 and HM-801 and concluded that I can keep my 801 and save the money for other gadgets (ordered a new 801 spare battery and charger).
Maybe my own ears preference, but it is very difficult to find a DAP that can play songs and music with analogue sounds - which only HM-801 comes very close to it, yet with details and soundstage. DX100 is very analytical and clear, but it is like most modern players. If you already have a good iPod, you can probably try out the Fostex HP-P1 or CLAS, as they both generate very analytical and clean sound and good soundstage.
Sold my Fostex quite sometimes back so can't do direct comparison, but to me, HM-801 sounds nicer and smoother.
Anyway, if you are upgrading from a iPod, you will definitely not be disappointed with DX100. It is one of the best DAP available, and you can't get a HM-801 any more since it is out of production now!