if you read fengwei007's review in post 1 and change the AK120 with the Colorfly C4 and the HM901 with the HM801 thats exactly how I feel for my C4 and hm801.
I actually don't like the words analog & digital as descriptions for the sq of DAPs but this is my subjective impression (it's only if directly compared to the hm801 - if I didn't have the hm801 I would never say that!)
I bought the C4 first immediately after I heard it at an exhibition and was highly impressed by its great sound quality. It is a truly fantastic DAP, has everything you wish - clear & transparent sound, great soundstage with numerous output options and I enjoyed it very much. However I wasn't drawn to the music as much as I hoped. Out of curiosity I bought the HM801 and knew immediately that it sounded right for me. Every song is a pleasure and I find interest in music genres I never thought of before (and that's the most important thing for me)
If you google the headfonia review of the colorfly C4, it has a better and more thorough comparison of the 2 DAPs and that's exactly how I see it.
However, although I think the hm801 sounds perfectly natural for me, many people claim, that it has a coloured tuning with an intended treble-roll-off. Still, I like it that way as I have no sibilance or any issues with piercing highs anymore (my phones are Grados and Hifiman He400).
My headphones are listed in my profile btw, and I like the hm801 better with all of them. But bear in mind that all my headphones are very efficient and I didn't try it with speakers or low efficient phones. It could be the other way round with other phones and people with different preferences, so YMMV