I remember a list of the amp cards planned for the hm-901 where one of the cards was a mimic of the stock amp card of the 801. It seems that you can have a better dac than the 801 but with that sound signature that some people love in the 901 using that card. If you love 801 that would be a great option.
You are right. There was something about a HM-801 amp card for the 901, but is has be very low output impedance ( > 1 Ohm) then, which none of the 801 amp cards are (respectively 10, 18 and 32 Ohm). However, if a warm sounding IEM amp card with less than 1 Ohm output impedance shows up, then I might be tempted.
I should add, that the warm sound of the HM-801 is not (only) in the amp section, it is surely in the DAC section (also). The Butterworth filter after the DAC chip is the cause of this, I think.
Edited by LarsHP - 7/18/13 at 7:52am