Anakchan kindly lent me some of his gear and I already have a couple of great DAPs on hand, so I thought I'd do an ongoing shoot-out between them.
Anakchan lent me:
HiFiMAN HM-901 with balanced card.
Sony ZX-1. Getting music on to this will be interesting, but I'll figure it out.
Cypher Labs Solo -db and Duet.
I already have:
Astell&Kern AK240. Mine. I have already made a balanced "tail" for my headphones and have more cables on the way.
FiiO X5 (on loan as part of the World Tour).
I'm waiting on a couple of WyWires cable sets and I need to make a couple more adaptors so I can compare amps, eg: The balanced out of the HM-901 and AK240 vs. the Duet, but I have most of what I need on hand already.
I'm quite familiar with the X5 and AK240 but I've only had one listen with the Sony (in comparison to an AK120) but the HM-901 is new to me.
Preliminary impressions shall be posted soon...
Edit: Here's my summary (which forgot to mention streaming with the Sony):
This is where things are looking now:
The AK240: You are paying for a DAP that has better SQ than anything else, to the degree that it rivals desktop rigs. Unlike anything that might come close, however, it actually will fit in your pocket and power headphones quite well that it has no right to be able to do so given its size.
Best things: Outstanding sound, UI and design quality.
Worse things: Price! Balanced adaptors and excellent recordings required to be of any value.
The ZX-1: Given it is cheaper than an AK120 and, by way of being a fully-featured Android device with an excellent UI on a large screen, this might totally win if it weren't for the lack of memory or a removable SD card and the strange lack of volume. It also has something of a bright, sometimes annoying sound.
Best things: Large screen with excellent Android UI and thin, well-thought-out case.
Worse things: Lack of expansion. Weird volume limit. Slight harsh sound.
The HM-901: For its price, it might win on sound quality and capability over the Sony, but the scroll wheel and UI put me off wanting to use it. If I didn't have the AK240, I'd want to listen with the HM-901 more than the others by far.
Best things: Most engaging and listenable sound (ignoring the AK240). Balanced card is great with full-sized headphones.
Worse things: Chunky, clunky, 1990's UI. Balanced adaptors required.
The X5: A class act considering the price. It really needs playlist support and it would be almost perfect with IEMs. Add an amp for more expensive full-sized headphones. The value king by far and lacks very little in enjoyment when listening.
Best things: Cheap, but quality design both with software and hardware. Excellent sound for the price.
Worse things: Doesn't drive full-sized headphones well. No playlist support.
Round 2, June 2014:
FiiO X5, Astell&Kern AK240, Calyx M: