Haven't compare uDAC to Extasy but Cowon D2+. using SRH840. uDAC has warmer mid, depend on what type of focal you listen it can good or bad. however uDAC is a little recess in the vocal, particular the female focal. recess with warm mean the airiness and echo is less to make more up-shifted emotional lacking in some songs. if the music itself is already U shape then it can be slightly harder to feel the singer. Singer is further and less "high". overall, uDAC sound is on the heavy side.
There is a Japanese song by Flipside called "Only my railgun" which people can try.another song I test is by Aya Hirano called "ElecTriCk" both foval sound less engaging with uDAC+Srh840 due to laid back and warm mid.
This is combination with SRH840 so please take the nature of SRH840 into consideration as well (also referred by some are laid back with punchy bass).
Looking at your first post I see you have Icon Mobile and ER4P and feel too bright of the sound. I have PFE (mid and high emphasis)which is closer sound to ER4P than UM3X or SRH840 while I try the same song. it bring back the singer quite a bit, although the bass become less prominent, the airiness of female vocal is much better and closer. overall uDAC will be better match with ER4P than SRH840 or UM3x (not saying these two match bad but ER4P or FPE is better for genre (anime song) I listen most.
At the end it is more of synergy of equipments, music style and personal taste. unless you can get super balance headphone, ruler flat DAC and amp, golden ear (mine is worst than rust >_<) you won't get perfect balance sound especially most headphone are not true neutral. one should really tried different equipment personally or read ahead to match their equipment (eg UM3x to my ear match better with Sansa Clip+ while PFE better with uDAC)