I purchased the X1S after the various shortcomings of my EMU 0404 became intolerable. The 0404 had great flexibility and served my needs for about 5 years before pot noise and, most egregious, frequent dropouts settled in. Installing the X1S was a snap although the user manual was obviously not written by someone fluent in English. Changing the filter setting requires continuous depression of the input button until the desired LED lights red.
My HD600 phones can now finally live up to their well-deserved reputation. The bass is much tighter, mid-range is fluid with very well defined positioning, and the highs are liquid. Anna Netrebko sounds like she's in the same room.
My only gripe is about the architecture. There's an Audio Out connection that I had assumed would allow the analog output of any selected input to be routed to desktop speakers. That output , however, works only with the output of the DAC - any device connected to Analog In is not connected. Also, the level of that output is always full line level.
Reviewed by: Charles Domingue from Sammamish.