I've used a couple of portable DAC/amps with AKM chips and others with ESS chips, they sound different and in close line with how their characteristics are often described. The AKM devices also sounded noticeably warmer than using the headphone socket on my phone. I now use two DAC/amps from IFI mostly, one has Cirrus chips the other has Burr Brown, similar but not the same sound. I don't claim that the chips are solely responsible for the sound difference, manufacturers may voice their products in some way, I would expect this in a competitive market.