The DAC is enough just for the decoding capability. The thing is though you have to note that in smartphones and other general purpose devices, the audio chip has not just a DAC but the output stage of the chip is usually a headphone driver stage. Plus you have volume control and in some cases there can be noise if you have to set it to an output level that matches 2volts as on wall-powered DACs.
In your specific case though since you're using IEMs and the Note5 measures well enough, with no problems on output impedance either, there really isn't much to gain from adding an external DAC-HPamp unit, not to mention you'll make the whole set-up bulkier. Might as well save the money and put it towards a headphone for home use and a desktop DAC-HPamp that can work with USB audio via OTG out of the Note5. Kind of like what I do with my Note3.
On the go, office, etc
The rig in my bedroom