A strange development. I have just replaced the DAC+ in my Zynthian with a DAC+ ADC.
I checked the datasheets on the Hifiberry website to refresh my memory about configuring balanced input. That information no longer appears in the datasheet. Well, I submitted a query and received a reply from Daniel.
According to Daniel, the earlier information was a “mistake” and the DAC+ ADC does NOT support balanced input. This will apparently be a feature of the upcoming (and likely more expensive) DAC+ ADC Pro. A little disappointing if this is correct.
For microphone input, in any event, I would probably prefer to use a proper microphone preamplifier, giving complete control over the gain, and phantom power for microphones which need it. For balanced line level input, I could implement a simple passive solution using transformers (I have a pair of nice Lundahls unused in a box).