Well I owned the unit since Dec 2016 but never once used the phone jack.
It is the 2016 version of 13' screen with touch bar and 2.9GHz, Intel 6267U 'Skylake'.
Today my stupid Chinese desktop DAC/Amp Yulong DAART Canary was dead with some serious hums and buzzes, so I was forced to use the laptop's phone out since my portable amp had run out of battery.
To my surprise, the overpriced laptop sounds darn good! No 'warm' distortion present as with the 10-Ohm Yulong DAART Canary.
It sounds pretty much like my transparent sources, say, sources with zero-ohm output impedance.
(I personally believe the main culprit for distortion is output Z, this is what makes tube amp sounds warm, IMO.)
Speaking of power output, which is the most important for me. Many sources on the net including this one say MBPs generally have 2Vrms max output. It can push my 250-Ohm, 96dB/mW Beyers and 62-Ohm, 106dB/V AKG K7xx to at least 90dBSPL as (measured by an iOS app) at max power on average music that's not subject to stupid loudness compression, and I'm quite sure it can go a few dB louder on tracks with brick wall compression. On very quiet tracks eg classical recordings, AKG K7XXs are loud enough, but DT880s can be very slightly too quiet to my liking. I'd ask for a dB or two more.
I measured the maximum SPL out of AKG K7XX using a 1KHz test tone at 0dBFS and found out that the SPL was around 98dB. At 1KHz, the AKGs have around 66Ohm of impedance, so 90dB equals to ~0.2xVrms, and 98dB equals to 0.4xVrms. On DT880s, the same file plays at around 93-94dB, which needs almost 0.5Vrms. So I guess the most headphones should work fine with it, at reasonable volume. Even the stubborn planar HE6s need exactly the laptop's limit 2Vrms to go 95dBFS. This indicates the laptop is pretty efficient, even for the more demanding headphones at <90-95dB on test tone or <80-85dB on music. I think it's powerful enough for most (my interpretation of 'most' may differ from yours) headphones on the market.
One compliant here is that it hisses on my very sensitive JH Michelle, but from what I could remember the hiss is less loud than that of my iPhone 6s on the same earphones. I sold the IEMs so I couldn't compare the hiss, since most of my current cans aren't very sensitive and efficient and thus are dead quiet on this stylish notebook.
notes:
I decided to conduct a blind test (at matched volume, calibrated by using test tone) with the laptop and Xduoo X3,
a pretty transparent DAP, and failed to tell the two apart. So I had concluded for myself that the laptop's amp 'design (ie specs)', at worst, is much more decent than my $250 desktop DAC/Amp.
I do not have the equipments necessary to properly measure its audio performance for the sake of objective evaluation, but I hope in the future someone here with the luxury would be interested in doing so as much as I do and measure this beautiful and capable machine.
Apple for sure has way more intelligent minds than audio companies do. I trust their products. I think most of their products sound reasonably decent, objectively speaking. Especially my iPad mini sounds quite great and
identical to the 2016 MBP(TB). iPhone 6s on the other hand, sounds a bit strange on most sighted sessions with the 10-ish Ohm JH Michelle, with tendency towards warm side, and I blame it on its 5-6Ohm Z out.
