In my just posted reply to
@Igordit I've just noticed something. In the warning they state:
The adapter they are talking about is the one they've specified for outputs - but it leaves the cold terminal unconnected. I wonder if that could be a source of the loss of SINAD when using it for an input.
Two problems - the low impedance shield is not used for the analogue return - which means the impact of a ground loop is worsened, and secondly the cold input terminal is left floating and able to pick up any interference.