Good point, I don’t actually know if the DAC Output has a common ground (single ended).
Once you get to the “good stuff,” you can find good balanced and single ended stuff around the same prices. Also, you can just make an SE Output more powerful, so power is another non- factor for choosing between them. Supposedly, balanced has less crosstalk between the left and right channels since they have separate circuits, which I would assume separation between channels would be better heard in headphones than speakers, but still monoblocks and essentially “balanced” setups for speakers are well regarded too. There might be other things to it, but as a non-engineer that’s how much I’ve picked up so far.
Essentially, I look at balanced as a physical high-gain option, so the SE outputs can have low background noise for IEMs, while the Bal outs have more juice for full-sized headphones (4x as much in the case of the ZX300A). And if I’m getting an upgraded, custom length cable, the price difference between SE and Bal cables is negligible, so why not? Sometimes, with Balanced, it seems like the sense of soundstage is deeper, and even notes playing equally in both headphone drivers seem to be better separated, but it’s a small thing (better cable and better amp design makes a bigger difference than two equally good SE/Bal setups).