The picture above shows that you can use a Fiio E17 with your iPhone 7 and 7 Plus.Playing CD quality music from your iPhone. Also internet Radio stations improve a lot in audio quality. You have to connect your iPhone to a +5V power source or external Li-ion power pack. And you have to switch off USB charging inside the Fiion menu. I do not know if older iPhones like the iPone 6 (+) work as well.
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aiff 96kHz 192kHz 16bit 24bit DAC USB 3 Camera Adapter Aptx Apt-x A1619 TS-BT35F18
iPhone adapter.