With the X1, where do you 'fall' with regards: what is (may be) responsible for your preference of it, since it is more than just a DAC?I dont think any one element can be identified as the reason for my preference for the X1. It is just a very well designed and implemented unit. I know that the Lumin streamers are very good (I also have a U1 mini), the ESS 9038 dac chip is capable of sounding great (I was less impressed with the previous generation of ESS dacs), the X1 has a very high quality linear power supply, and the output stage uses the excellent Lundahl transformers. It is finished to a very high standard. All of these factors combine to produce great sound.
The sound the X1 produces is dense and colourful, perhaps slightly warm, as well as being fast and dynamic. This contrasts with the slightly thin and cool sound of the Chord DAVE/Blu 2 which I owned for a while, and which is not a sound I typically enjoy. The DAVE did have more apparent detail, but it was an illusion caused by the leanness of the sound and overemphasis of fine detail. The X1 has all the detail, but it has a fuller, more natural sound so that detail is not artificially emphasised.
The Metrum Pavane I owned at one point, which is an R2R dac, was also very good, and had a similar sense of tonal density and richness. But it sounded a little slow compared to the ESS based dacs (and the DAVE) and was, to my ears, lacking slightly in dynamics. The X1 seems to combine tonal richness and dynamics in a way that is close to ideal. I'm sure that there are better sounding dacs out there, but you would probably need to spend crazy money to improve on it and achieve that last 1% - maybe.