The $1,300 Astell&Kern AK120, which launched last July, is a pocket hi-fi masterpiece. The new Astell&Kern AK240 promises to take portable music playback to an even higher level. The new player, which the company expects to begin shipping in March for a price beyond $2,000, will feature 256 gigabytes of onboard memory—compared to 64 gigabytes for the AK120—plus a microSD card slot allowing an additional 128 gigabytes of storage. Like its predecessor, the AK240 will support music files with resolutions …