A differential DAC configuration is essentially like a balanced circuit where one DAC is "going positive" while the other is "going negative". This configuration lends itself to balanced audio connections since no additional conversion is needed to create a balanced analog output.

Differential configurations have some noise and distrotion advantage over single ended configurations, but I seriously doubt that anybody, including myself could hear the difference in an A/B blind comparison. A common way to design a differential DAC configuration is to use a regular stereo 2 channel DAC for each audio channel. The left and right channels of the DAC are used for each polarity of the single audio signal.

I would much rather have a really good single ended DAC configuration than a lesser quality differential one that was just marketing driven.

Like all things, what matters is the final sound, not the number or configuration of DACs or DSPs. A good designer can make a combination of good quality parts perform better than premium parts in the hands of a less talented designer. A great carpenter could build a better house with an el-cheapo hammer than I could with the best hammer in the world.