Pros: Connectivity, Price Reduction, SQ, UI
Cons: "High Resolution" support
I use the 30pin line out dock on my iPhone 4s as a portable source. As a portable source the iPhone 4s makes an excellent choice for lots of reasons that I'm not going to explain in this review. Here are the highlights that do it for me. I'm going to make the case that the iPhone 4s make a great dedicated lower cost portable source. The best function the 4s has going for it is web connectivity. I want to listen to the 'Ex Machina' Soundtrack By Portishead’s Geoff Barrow And Ben Salisbury right now. I can do that with a smart phone! I want access to the millions of tunes in the Tidal music catalog I can do that to. I can load WAV files onto the 4s granted the iPhone won't do 192khz / 24bit or DSD... well la dee freaking da, I don't care. I can't consistently tell the difference between 16bit and 8bit tracks. Try going to audiocheck.net, select the tab blind audio test and take the '16-bit v/s 8-bit Blind Listening Test' for yourself.
Soundexpert.org has the sound quality measurements on 4/4s, I realize that the measurements and numbers are far beyond anything the human ear can quantify, I know my ears can't.
I do think that using the line out dock is the way go. Bypassing the on-board amp circuit and using a dedicated external amp offers superior sound quality but you already know that.
The iPhone 4s will soon be three generations out of style and the price will reflect this. I think this is a steal that offers a very high price to performance ratio.