What are you playing from your iPhone? If its lower-quality files like MP3 or Spotify, your Lightning to RCA will probably be fine. If you have CD or higher res quality files, you might consider an inexpensive DAC, like the AudioQuest Dragonfly Black ($99). You will also need to get a Lightning to Camera adapter (to plug in the DAC), and then 3.5mm to RCA adapter. The Dragonfly will be a noticeable improvement over the iPhone DAC. Apple sells two different camera adapters. Get the one with the additional Lightning socket so you can charge your phone while listening to music.
iPhone to NAD 316
I have an iPhone with a lightening connection and an NAD 316BEE v2. I believe that it is possible to hook them up and play music from the iPhone over the amp. I can either get a lightening-to-RCA cable (my preferred method) or lightening-to-3.5-headphone jack, the female version of which is located on the front of the amp. Which one will work? Which one is best? I guess the phone is outputting a digital signal. Do I need a DAC before it reaches the amp or will something—the cable, the amp—handle that? Many thanks.