Problem is that I prefer the sound of 2 of my different one piece solutions to your stack so your minimum is very different than mine. It doesn't matter which of us is wrong or right but the 2 piece stack as universal minimum is a nonstarter. AK120 needs no further FW updates to be great and my Anniversary 3 UI works well enough for my needs that I ignore my Ipods and Sansas and it has a VG internal amp stage. I don't even think the e17 improves every Ipod. Internal dacs have a huge advantage of not needing to be reclocked or defeat added interface jitter. Full size phones are another matter and carry size already chosen so an amp is appropriate... but for IEMs, one piece if done well, is the right way to go.
Agreed on your point about it being a personal choice. The AK120 looks like a great player. When matched up with the right headphones, I'm sure it sounds great (have not heard, so cannot comment on its sound).
My post was really more about the design space than the final answer. A two-device solution gives flexibility right now, but the flexibility might not be needed depending on what headphones you use, and a single device has plenty of advantages (a single battery to charge is another big one).
For me, the E17 does improve my iPod mini because I got the iPod free from a family member after the headphone jack was worn out (does not hold a headphone plug in very well any more). That alone is an improvement, but also the low output impedance of the E17 helps my Sony XBA-4 IEMs work best.