I appreciate the some of the comments here
Yesterday I went to listen the hm-901 and made a short comparison with my DX100 and C4
the DX100 seems to be kind of similar to the 901 sound overall as they use the same DAC chip ES9018(but 901 has two), while C4 sounds very different to 901 and dx100 in terms of imaging and soundstage
I found the 901 has a more punchy bottom end to the 901, but 901 does not lack bass, it has a deep and dynamic bass, however it's a little bit tight than the 901s
C4 does not have the bass quality compared to 901 and dx100 but it's also very good.
the human voice from 901 is absolutely amazing, it's very engaging and forward. I can clearly distinguish that the vocal density from 901 is better than the dx100 a bit. dx100 produces a relatively flat mid range, so from the point of realism i would go for dx100 coz it sounds like real human voice although it's not that engaging compared to the 901
C4 has a smooth and forward mid range, I feel a little bit grainy, and a little bit more spacious sound to the 901. I like the vocal of C4 best.
All of them have good highs, but the dx100 will sound more airy than the other two, as it has a slightly better extension on the top end. So dx100 will have a little bit sparkling highs than the 901 and C4. The soundstage is really wide on dx100, C4 is also good as well. The 901 has a more sort of refined sound signature overall, it's neither dark nor bright, so i would say 901 has the best coherence among the three. Dx100 is a little bit "V" shape but it's not clearly a disadvantage as u will get more spacious sound, that makes the soundstage wider and i can hear the distance between different musical instruments when listening to Jazz or classical
What was the 901 amp board you demo'ed?