Players that are digitally balanced use separate sets of D/A converters for the inverting and non-inverting legs of the balanced output. The single ended output is usually derived from only the non-inverting leg of the balanced output.
Thus the single ended output only uses half the D/A converters. This results in a bit higher distortion on the single ended outputs.
A few players derive the single ended outputs by combining both legs of the balanced output, and should sound similar either single ended or balanced. I know older Wadia gear did this, but I'm not sure about others.
Players that are not digitally balanced generate the balanced output from the single ended output (usually via a phase splitter) and may actually sound better single ended.