With regard to USB Audio, iOS and digital clocking, which device should be set as clock master?
Normally that is straightforward to answer - the clock closest to the AD or DA converter is the best choice, assuming the converter device is good quality.
IOW, the iCA4+ should be clock master for digital audio.
However, I don't know much about USB digital audio in iOS - is the USB stream re-sampled (and therefore also re-clocked) by the iOS device via ASRC?
Is there any circumstance where iCA4+ users would select an iOS device as digital audio clock master?