Cmk - the DAC-1 converts single-ended to balanced at the output drivers. I would not call this a balanced DAC, but I suppose there are other interpretations.
Steve I'm not technically inclined, just a bit of tech knowledge, so I can't tell what's really balanced or not, but I do know this, the Benchmark's XLR outputs are a quantum leap over the RCA. Something which 2 others I know have heard, and confirm the same findings.
Since you obviously know more about the internals of the Benchmark, maybe you could shed some light on why there's so much difference between the two?
Bob_reynolds - when I first started modding DAC's I put no additional resistance on the outputs. What I found was that with high-Q or low-loss cables connected, this evidently caused transmission-line type reflections on the cable which could take a while to damp-out whenever there was a HF transient in the music. My theory is that these reflections cause the output drivers to go non-linear at times, which affected the audio range.
If I approximately matched the characteristic impedance of the cables (like you would do in a RF system), the sound improved dramatically at the high-frequencies. Most analog cables are in the range of 75-120 ohms characteristic impedance, never as low as 30 ohms.
There are other engineers that have tried this and reported similar results.
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