megabigeye
Headphoneus Supremus
I edited my original post, but I'm not sure I got it right. Sorry if that's all stuff you already know.While Technically true. They all also have 3.5mm Line In, 3.5mm Balanced Line In. Or, Micro USB. I would go with 3.5mm connection most likely.
yong_shun is correct. As I said in my edit, iOS devices with Lightning connectors don't have an analog line level output-- only headphone and digital. Amping the headphone output is only going to make it sound worse, not better. You could do it if you want, but I wouldn't spend the money on a DAC, just an amp.