What's a "quack DAC" and who thinks it is more important than what buffer is used to actually drive the headphone load? 
"quack DAC" lol!

I'm guessing it's 4 DACs in parallel. Maybe you can get better accuracy that way, I don't know! Probably mostly audiophoolery. Agreed about the output amp/buffer being more important....
[Edit: Quad DAC is essentially a marketing name for an ESS brand DAC/Amp chip. It features a 32bit 384 kHz "quad" DAC stage, which is obviously way overspecced for audio frequencies. ]
My criteria for a smartphone are:
1) Must have SD card slot for big FLAC music collection.
2) Must have replaceable battery, and must have availability of extra large capacity batteries!
3) Must have headphone jack to drive headsets and classic car AUX inputs. Bonus for higher quality audio circuitry!
As a result of this thread I've been looking at what's avaliable, I've ended up ordering a V20 to have a closer look at - on paper, I like it a lot for my use case!
The Galaxy Xcover comes close, but because nobody makes extended size batteries for it (yet, at least) it isn't ideal for me. I'm guessing that this model will catch on eventually, it is probably still a little too new to have developed a supporting ecosystem of extended batteries!