I drive the headphones Jade II with the little D10 since the beginning and I like the couple. Sounds slightly different from the L300, with some recordings I prefer the Jade, e.g. classical and some jazz, with the majority of other recordings and music such as Rock prog prefer the L300, especially when drilling trebles are in the record (cymbals and trumpets can hurt badly).
Then I bought the Hifiman amp because I was curious, it sounds quite different from the D10, has much less extension upper and lower, maybe is made this way in order to tame the highs, however I don't like it even with poor recordings, adds a sort of middle bass that annoys me, D10 is more trasparent, for me here: the 'smaller' the 'better'
It is in line with other HFM amplifiers I heard, nothing special and dims even its own headphones, Jade II can sound better with a competent amplifier, about the quality, based on my experiences with previous Hifiman cans I'm not expecting they last many months, will see.