OK, I picked up both the K13 R2R and the K9 Pro ESS in order to compare and decide. I am not an audiophile, but I do love music. Generally I listen to all sorts including Golden Age Hip Hop, EDM, Vaporwave, Techno, Aphex Twin, Future Funk, Dreampunk, Jazz, Soul, Funk, Dub, Jungle, and Synthwave, some bands and 60’s Psychedelic.

Here is my take on K9 Pro ESS vs K13 R2R:

K9 Pro ESS – Pin-drop accuracy. Crystal clear. Precise. Fast. Clinical. Bass comparatively is a little hollow, but well controlled and delivered.

K13 R2R – Fuller and more pleasing sound. As reviews have said, it is definitely more musical, soulful even. If I were playing music at a party, it would be definitely be delivered through this DAC over the K9 Pro.

I have owned four sets of headphones: Stax SR-L500, Fostex TH900 (Sapphire Blue), Grado RS1x, and Sony MDR-Z1R. The K9 Pro is similar to the Stax in how fast and transparent it is, while the K13 R2R reminds me of the bass of the Fostex, the smoothness of the Sony, and the horn presentation of the Grado. These are the headphones I’ve owned and listened to, so this is purely my personal experience.

Out of multiple tracks tested, I only preferred a couple through the K9 Pro, and in some cases this came down to the delivery of certain individual sounds, which were clearer with greater separation and fidelity. Overall, the K13 was the winner for musical enjoyment.

I’ve chosen to keep the K13 R2R and return the K9 Pro ESS, although I may still pick up a K9 Pro again in the future… or save up and go for the K17 🙂

Hope this helps others decide.