Audiophile Setup with an Iphone 7

Apple Airport Express or Google Chromecast, using their optical outputs?

The digital outputs of the Apple Airport Express or Apple TV and of the Chromecast Audio are bitperfect, and hence have no sonic signature. That would come from the DAC that one uses. An external DAC may improve the sound, but the inbuilt DAC of these devices is actually pretty good. The question here seems to be how portable the system has to be.

Thanks for the link. I read the Darko piece, but note (not for the first time) that he presents no hard evidence for what on theoretical grounds is a pretty implausible argument. I honestly do not think he is someone to take very seriously. Anyway, that is my take. See here for what I think is a far more solid review: http://archimago.blogspot.nl/2016/02/measurements-google-chromecast-audio_27.html