Their in-house made r2r solution is better than the one in most r2r dacs. They supposedly really improved the design.
This is what they say about it-
"
HIFIMAN’s Hymalaya Pro consists of an array of highly accurate resistors that use a “ladder” method of conversion. This approach converts the digital signal with maximum accuracy and overall musicality. Signal-to-noise ratio, total harmonic distortion, and energy consumption are at their musical and efficient best. Hymalaya Pro supports the common PCM signal transmitted by the most common IIS (Integrated Interface of Sound) audio interface, with a maximum 24Bit resolution.
The EF600 includes two Hymalaya Pro modules for unsurpassed sonic output, especially when compared to the more commonplace PCM1704k module. The Hymalaya Pro, with the added support of a new algorithm and 0.01% precision resistors, reaches a THD (total harmonic distortion) rate of -60dB 2%. In plain English, distortion is reduced to a previously unheard of low with no audible distractions."