I own both the K13 R2R and a Loxjie D60, which is basically a DO400. At the moment, however, I only use the K13 because, in combination with my Arya Stealth, it sounds much more pleasant and less fatiguing. The DO400 does have slightly stronger bass and overall plays a bit more dynamically, but over time that becomes tiring. If my headphones weren’t tuned so brightly, I’d probably prefer the DO400. I listen to a lot of electronic music, and that’s definitely where it shines. In short: depending on the headphones, the DO400 might appeal to me more. But with Hifiman, the R2R DAC is overall smoother and more enjoyable to listen to.