Cool link! Regarding music players, I personally switched to simpler/less-costly solutions because I do a lot of hiking and I can get caught in sudden storms or just end up dropping things. Along those lines I tried a lot of agptek devices and they've been really good.
I suggest an external DAC for your phone unless you have very specific requirements; I use a iFi iDSD Nano (which is no longer being made, but there are equivalent models), what's best for you depends on your use case (what kind of headphones or speakers would you use?).
[1]: https://kottke.org/19/07/sonys-proto-walkman-that-went-to-th...
Off-topic question:
Since this is a thread on Walkman I'd like to ask you on any dedicated music player that you'd recommend?