GoldenSound of The Headphone Show listened to Astell&Kern's SP3000 and heard imaging that was "laser precise." Astell&Kern makes dedicated music players, and its central idea is to put flagship converter chips, often several of them, into a body that fits in a pocket. The converter, or DAC, is the part that turns a music file into an audio signal. Running several in parallel can lower the background noise, and What Hi-Fi?'s reviewers heard more clarity and subtlety from the SR35 with all four of its chips working than with two. The flagships also keep the left and right channels unusually well apart. Across the range, What Hi-Fi?'s testers hear a "full-bodied, entertaining character," and GoldenSound found the SP4000 "extremely close to neutral." Astell&Kern suits listeners with good in-ear monitors and a large library of their own files.

Moon Audio calls the SR35 "a fantastic entry point," and it won one of What Hi-Fi?'s 2025 Awards. The magazine's reviewers advise leaving it in Quad DAC mode unless the battery is low, and they heard a Sony MDR-Z1R sound "clearer, bolder and more precisely drawn" from the balanced jack, so use that one if your cable allows. The step up is the A&ultima line. GoldenSound found the SP3000 aimed at in-ear monitors and called it "an absolutely terrific device" for easy-to-drive headphones. The SP4000 roughly doubled the power, and he ran an HD 800S and a Meze Empyrean II from it without trouble. If your headphones are full-size and hard to drive, look at the KANN players, which put power first. Steve of Bloom Audio heard no hiss from the KANN Ultra with a sensitive Campfire Andromeda, while with a Hifiman Arya it would "really hit like a desktop system."

Astell&Kern began as iriver's entry into high-end audio, and Stereophile's Michael Fremer calls it a move upscale for the Korean maker of MP3 players. The name joins the Latin word for star with the German word for core. When John Atkinson reviewed the first player, the AK100, for Stereophile in 2013, the top iPod still played nothing beyond 16 bits and 48 kHz, while the AK100 handled 24-bit files at up to 192 kHz. The AK120 doubled up on the AK100's DAC chip, and dealers told Currawong of Head-Fi that AK120s were "flying out the door." Michael Lavorgna of Stereophile called the AK240 of 2014 "the luxury choice in high-resolution portable music players." Currawong heard one with Sennheiser HD800s at iriver's offices, bought it, and said it could stand in for his home rig. Atkinson later measured the SP1000 of 2017 and called the result "superb behavior for a digital product that runs off a 5V battery." Moon Audio now names Sony and Astell&Kern the two dominant makers of digital audio players.