GUYS!!!! I have the retina macbook pro and i have to say that the internal D/A chip and amp are actually very good. It was a major step up from my HP Dv6tse laptop.
I ordered the HRT streamer II+ two weeks ago and returned it because the improvements it provided were marginal at best when compared to the retina MBP's onboard chip (only a minor improvement in soundstage and the slightest of improvements in detail). I use K702's and the onboard chip is capable of driving them decently. I still use an amp though, for that extra oomph.
In case you thought my Streamer was faulty, I checked with the previous generation macbook pro. The difference in quality in that case was massive. Think about how the retina MBP's speakers sound significantly better, even with a shrunk chassis...The onboard sound card was revamped and the results are amazing. I have no need for an external DAC for the forseeable future.
I really dont know if your retina MBP is faulty, but the sound coming out of mine is really really good. Surprising actually. On second thought yours might be faulty if your iphone 4 does a better job
Edited by Ampeezy - 10/11/12 at 5:03pm