Hi!
Are you sure the CS4398 doesn’t have a single channel mode? Several years ago I was looking at its datasheet and remember this was an option configurable through its firmware. The dynamic range was specified as 120dB (it was a top-spec chip at the time) and 123dB in a single channel mode. Perhaps it was a misprint in the datasheet but I doubt it.
There would be no point in using a dual-channel (stereo) chip and using just one channel for, let’s say, the left channel and then another chip for the right channel. You’d be using twice as many chips as needed! 😊
If you look at a photo of the D/A-analogue section, it is laid out very elegantly, even beautifully, and it does look like a differential circuit.
But I don’t know, I am not an electronic design engineer. It’s an interesting question to be sure!
Cheers,
Antun