In general all newer iPhones and iPads (with updated software) works with USB DACs, however for some models the phone thinks the DAC requires too much power. This is because of the power requirement which is reported by the DACs USB chip, and not the actual power requirement. For TE7022L (used in most versions of the the Sabre DAC) this is reported as 500mA, even though the actual power consumption is well below 100mA, and this makes the iPhones/iPads not want to support it. However it will still work if you put a USB hub in between, as the power requirement will be sent to the iPhone in the same way then.
iPhone 6, iOS 8.4.1