Doc - you are correct. My mistake. A Lightning to USB cable should work. Another option would be a Lightning to USB Camera Adapter (see link here; supports USB 3.0) that allows charging while the device is connected. You will need a USB power adapter for the charging. A USB A to B cable will connect this adapter from your device to the DAC.
https://www.apple.com/shop/product/MK0W2AM/A/lightning-to-usb-3-camera-adapter