Good question. My ODSX is such a DAC, with 4 identical separate channels going to balanced outputs. I generate SE RCA outputs, by only using 2 of the 4 channels. I do this because adding another stage that subtracts the balanced signals adds too much distortion and noise. My DAC has a single output stage that does everything (I/V, gain, Analog filter, compensation) in order to keep the noise and distortion low.
I don't recommend using the SE outputs from my DAC for the main speakers because they just don't sound as good as the balanced outs. I do have a buffer on the 2 RCA channels, so that one can use this to drive a subwoofer. This is to eliminate the additional cable and impedance load that driving both RCA's and XLR's would create.
The devil is in the details with DAC's. Most of them take the + and - signals from the D/A I/V converter stage and after a filtering stage and gain stage subtract them to create a SE output.
Another thing to understand with balanced outputs is that electronically created outputs are the rule in modern designs, not the exception. Unfortunately, these electronically created balanced signals are never truly balanced because:
1) the + and - signals cannot ever be exactly the same amplitude
2) the output impedance and impedance to ground can never be exactly the same
3) the amplitude of the + signal may not always be the same as the - signal as the amplitude changes, a dynamic effect
This is why it's important to consider transformer isolation with something like the Final Drive, Lundahl or the like. If the transformers are high quality, the SQ is usually improved over using no transformer. This is because they provide galvanic isolation of grounds, eliminating ground-loops, and amplifiers usually sound more live when driven with a truly balanced signal.
Steve N.
Empirical Audio