I bought after a review of many positive reports in Inet several months ago the A200p (initially on iPhone 5s now on iPhone 6). A real difference to the jack of the iPhone I've never heard my Shure 535 (EIA 470), but pushed it to my untrained ear. Although an improvement've always imagined, but in a blind test (someone else puts the Shure headphones) I could never tell what sounds better iPhone directly or A200p.
After I read more and more critical voices to A200p, then I have taken the trouble to investigate more closely. On Amazon, there are several reviewers who return the unit back as they notice any difference on iPhone. What struck me (before buying already should have noticed) is that many of the sites, the praises of the A200p simply intone only the official press release from Beyerdynamic embellished without really measure the hardware. There, the authors like to use then flowery terms of a sound of 'deep, rich, spatial, clear as if someone had removed a curtain' is.
If you researched a little further, one comes out that an iPhone represents only 44 kHz pieces. The A200 p but is capable of processing 96 kHz / 24 bit. The standard MP3s and esp. Every piece that you can buy from the iTunes Store, however 44kHz maximum. When playing a 44khz iPhone (since 4s) seems to be so but already top that additional hardware brings no measurable benefit. I hear this is definitely no difference.
So I started a HD audio self test with the iPhone 6. I have for 24 the album History of Michael Jackson acquired (30 tracks with a total download volume of 3 GB!). iTunes played the pieces also nice to play on my PC. But when transfer to iPhone's 6 then came the message that the 30 pieces were not synchronized because they have an unsupported playback frequency. Aha, so iTunes detects that the iPhone 96kHz / 24-bit can not play and refuses to transfer from iPhone! So further research on the net.
Solution: Player from a third party install (I VLC) taken. But then does no longer synchronizing the iTunes music library. You have to (ALAC, FLAC or whatever) to load files via the iTunes menu Apps' share on the iPhone (ie app-specific, for example, in the VLC player), which iTunes playlists are then naturally for naught, for mass data the method is not suitable IMHO.
The VLC plays but then beautiful, the material from (both directly on the jack output of the iPhone, as well as at the output of A200p). And here I dare to actually claim that a difference is noticeable!
Conclusion: For smartphones with poor DAC certainly a good choice! For iPhones it pays off only if one is willing to invest in high-definition audio. With 100GB of storage per piece of music can indeed any calculate how big his audio library on the iPhone will then be up to. Added to the complicated 'manual' synchronization effort of HD audio pieces coming to the iPhone (ie, esp. Of course not iTunes playlists in VLC).
Mir is the subject of HD-Audio currently frankly way too much effort with the iPhone, my A200p sold so soon used on Amazon, because it definitely does not bring any improvement in sound on the iPhone in normal pieces (iTunes store).
5 stars because of A200p basically a TopHW with great service is (esp. For mobile phones with inferior DA converters). 1 star deduction because of poor information policy of Beyerdynamic in terms of the added value of the unit on iPhone. What ultimately led me to a bad buy.
No comparison with the added value of the reasonable headphones / in-ear compared to the Apple standard headset.