The ASUS ZenFone 2 seems like the latest bargain for USB DAC users. This guy is using it with his ZuperDAC: https://www.indiegogo.com/projects/zuperdac-portable-hifi-music-anytime-anywhere#/story
It's been tested with a 128Gb Micro SD card. With the 64Gb version, you get the fast-charger and 4Gb of RAM, etc. At $299 shipped (US), it's very tempting. Has anybody any experience yet?