With iOS 7, Apple opened up the capability of using the Lightning to USB Camera Adapter to stream digital audio over USB from the iPhone 5 or 5S. This is a function we have been enjoying on the iPad since its introduction, and now it has finally come to our more pocket-friendly iPhones.
Like the iPad, the iPhone limits the amount of power supplied to an external device attached to the Lightning adapter. If the device attempts to draw too much power, the iPhone refuses to connect. The UHA-6S.MKII includes a charge enable/disable switch. When charging is disabled, the UHA-6S.MKII is powered entirely from its internal battery, and there is no worry of exceeding the iPhone power limit. Because the UHA-6S.MKII is not drawing any power over the USB connection in this mode, it does not drain the iPhone battery unnecessarily.
Using the Lightning adapter instead of an analog connection from the iPhone headphone output has the obvious advantage of bypassing the iPhone's internal DAC, allowing the use of the higher performance DAC in the UHA-6S.MKII.
The upcoming UHA760 also includes a switch for disabling the charge mode, so it can be used with the iPhone in the same manner. The UHA-4 does not have a charge disable feature, and unfortunately it draws too much power to use with the Lightning adapter.
The Lightning to USB Camera Adapter is available in the Apple Store: store.apple.com/us/product/MD821ZM/A/lightning-to-usb-camera-adapter.