I recently picked up the RWAK120-B from a fellow Head-Fier and have been trying it out using the Silver Widow TRRS-to-Kobiconn interconnect with the ALO Rx Mk3-B+ and Cypher Labs Duet amps. I've been extremely impressed, almost overwhelmed by the improvement vs. my old Cypher Labs -dB/Theorem 720 DAC setups; the details, resolution, depth, clarity, midrange presentation (more balanced sounding, less veiled; upfront presentation without being aggressive), and bass weight, nuance, impact, and detail being a tremendous improvement over the AK4396 Cypher Labs DACs. The RWAK120-B is probably by far the most nuanced sounding DAC I've ever listened to, with vocals having an absolutely absurd amount of realism/detail.
With all that said, I really enjoy the sound of the RWAK120-B, and have been playing it connected to my HD650s (balanced Silver Widow HP cable), K3003is, and IE800s. All sound wonderful through the DAC, although at times I feel that some 16/44.1kHz recordings can sound a bit "hot" with IEMs (haven't had a 24/96kHz+ or DSD file give me any fatigue issues with IEMs, only when playing certain 16/44.1kHz albums.)
The HD650 w/ balanced Silver Widow cable sounds absolutely wonderful with the RWAK120-B, by the way. With the CLAS -dB and Theorem 720, I've never really enjoyed the sound of them with the HD650s, and stuck to mostly using IEMs (K3003i/IE800) with the Cypher Labs setups. For the first time in a long time, I've pulled out my HD650s and have been listening to them almost non-stop with the RWAK120-B. Weird how the CLAS DACs give off a veil when compared to the WM8741 dual DACs in the RWAK120-B, the latter producing a more "organic" and lushly detailed sound that compliments the HD650 extremely well.
Other than the wonderful sound quality, unfortunately, the (RW)AK120 doesn't seem to want to work as a USB DAC, at least not with my mid-2013 Macbook Air (1.40 FW). I've tried both in bootcamp (Win7 x64) and Mac OSX Yosemite, selecting the iRiver USB DAC as the "sound output" device in both OSes, with no sound output coming out of my amp at all. It seems that in Windows, when I try to output audio to the iRiver DAC, the volume mixer seems to respond to the levels of the audio being streamed in the OS to the DAC, although both single-ended and balanced-outs on the RWAK120-B produce absolutely nothing. It is quite disappointing, and I think I read something in passing that this might be due to a weird "USB2.0" port issue? I don't get that. It seems like the AK120 wasn't really made for USB DAC usage anyway, as it lacks a dedicated ASIO driver (although it seems that iRiver recently developed an ASIO driver for the AK240?), and can't even stream anything higher than 24/96 in USB DAC mode, and is unable to pass 88.1kHz over, too.
Battery life with the RWAK120-B has been actually somewhat impressive, especially playing DSD files. It's nothing to boast about, but I got at least 7hours yesterday listening to a mixture of DSD, 16/44.1, and 24/96-192 files in balanced out to my ALO Rx Mk3-B+.
Does the AK100II/120II/240 act more like a full-fledged USB DAC? I'm not sure the AK120 could be considered as having a functional USB DAC aspect, IMO....
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