I remember when I got to try out the AK100 II at CanJam RMAF 2015. The sound was great and the design was typical iRiver A&K unique and functional. The size is nice, pocket worthy. We mostly used it as a source with digital out to feed music to desktop USB DAC's and amps. You can stream TIDAL on it if you have a wifi connection, but the wifi isn't as strong as a smartphone’s antenna and TIDAL won't let you store music offline inside the AK100 II. Up to 8 hours of battery life is about standard for DAPs. I understand the “prestige” factor that AK DAPs have; even if you didn’t know the “luxury” prices, you can hear it and feel it when you have the unit in hand.
Last week, I just received my Sony ZX300 I purchased. I think the combination of sound quality, powerful balanced output, 25-30 hours of battery runtime, and pocket friendly package is a killer combination.
It has a standard 3.5mm jack that drives my HD 58X Jubilee at about 75 volume setting out of 120, and it has the more durable 4.4mm balanced port that drives even my 300 Ω HD 800 pretty well with textured bass (EQ boost helps) and great detail overall, and a non-fatiguing signature. Usually, I don't bother to fully turn it off because it has a very battery efficient sleep/standby mode, and turns back on almost instantly (from off, full power on takes a few seconds as it rebuilds the song database, but it's still less than half the startup time of my FiiO X7).
The ZX300 doesn't have wifi, but I can stream Bluetooth to it from my phone or iPad (AAC, aptX HD, SBC, and LDAC codec support for wired-like sound quality and fairly low latency) without destroying the battery life of either device... Last night, I accidentally left my ZX300 in Bluetooth Receiver mode connected to my phone when I went to sleep (after playing with the ZX300 for a few evening hours), and this morning 10 hours later it still shows at least two bars of battery.
The ergonomics and tactile pleasure of this player are next-level. It is the perfect width and your thumb can reach the whole screen without stretching, like an iPhone 4. The dense weight, brushed aluminum, leather back, and matte glass touchscreen are all feels-great features and provide a positive grip and premium feeling. The attention to detail on the control buttons is amazing: on the curve of the side of the body, the buttons are slightly angled towards the back of the unit (interesting to wonder why), with the small power and larger volume + - buttons curved and matte to match the curve of the body, and the playback control ⏮⏯⏭ buttons flat and polished so the edges seem to stick out from the body, with a raised dot on the + and play/pause button, resulting in 6 buttons that are easy to distinguish by feel if you put your hand in your pocket. The custom UI is a pleasure to use, with a swipe gesture from each side of the screen providing intuitive shortcuts to song navigation and processing options, and quick response times and scrolling - this is a better interface than Apple at its peak.
I was trying to use Bluetooth output to connect my ZX300 to my 2013 VW Golf, but weirdly they weren’t able to find each other for pairing. I’m going to try again, maybe call customer support, but if it can’t connect, that would be a major bummer. I wish it used a more standard USB connector, though apparently the Walkman port has a line-out feature with the right cable, and at least it connects more securely with less chance of damage than the old Apple 30-pin iPod connector. I pay for Spotify and TIDAL, and the lack of support for those apps was the main thing that had me holding off on buying this for a year, but then a Sony firmware update added the Bluetooth Receiver feature which pretty much solved that AND makes a pretty nice sounding solution for my headphone jackless iPhone 8.
Obviously I made a choice between an AK and Sony, and I think the ZX300 specifically has dialed in my favorite set of features on the market, but hopefully I described the ZX300 well enough that you can read descriptions of the AK100 II and other players to decide for yourself what products are most attractive to you.