The Xonar Essence isn’t completely responsible as my DAC though. I do use the Musical Fidelity M1 DAC for the arrays. It is connected to the Asus ST card with an optical SP/dif connection as a slave.
I’ve made several comparisons between using the Asus ST and this M1 DAC. I can’t point out what it is but I do prefer the M1 DAC for the arrays. As my son put it, one sounds like a fresh band playing wonderful music and the other as a band that has done a 5 set song already and you hear the vocalist being somewhat tired. The M1 was the one that sounded fresh. The song he listened to is the live version of Hotel California by The Eagles. from their Hell Freezes Over album. It is one of his favorite songs, one that he listens to through headphones on a regular base.
While I wouldn’t describe it in a similar way, the M1 does seem to sound the most open and dynamic of the two.
It features several connection options, at the time that I bought it, I was mainly interested in the optical connection to be able to separate the ground of the PC from the amplifier.
Stereophile had a review of this DAC where it compared favourably (the measurements) to much more expensive DAC’s. The one I got is the upgraded model. That’s why I didn’t link to the review done back in 2011.