Sorry for the cryptic post. The sound had a kind of tearing or static quality to it - though there was no static sound between tracks. It was really unpleasant - I remember hearing something like it on early bluetooth earpieces when sounds like applause or crowd noise was coming through.
I realized today that after the O/S upgrade, Amarra was probably not running and I might have played through iTunes when the problem occurred. Playing through Amarra now, it sounds much better, but iTunes also seems better. The DAC, though, now reads 44.1, whereas it had been reading 348 and 352.