For compressed MP3 / AAC good

On my Roth MC4 amplifier KEF iQ30 compact speakers an iTunes Laptop (Windows 7) on Arcam rPAC competitors should make the integrated DACs from the iPhone 4 or 4S. The Roth MC4 is a hybrid tube amplifier, in addition to an analog iPod / iPhone docking input also has RCA inputs. In small quantities, my music (almost all directions) exists as AAC / MP3, but mostly it is with Apple Lossless (ALAC) with iTunes encoding of original CDs.
The rPAC I tested, as I read in sync Music on iPhone and rPAC and saw switched between the two signals at the amplifier.

For MP3 / AAC encoded signals, both with 128, 256 and 320kbit coding, the rPAC played clearly better. The stage was a little wider and the instruments sounded clean. I had the impression that the worse the quality of the encoding, the more difference in favor of rPACs was present.
When an Apple Lossless signal in which there are no compression loss, but I could no difference on the system described above and their own ears or my wife, who has also tested diligently listen between the iPhone and rPAC. I had the impression that the iPhone could improve the quality to MP3 / AAC signal, but produced the rPAC no further improvement. Perhaps it was only at the Roth amplifier and the KEF speakers and compact with another, better setup would be a difference there? Or perhaps our ears are already over? ;-)

I have the 199-euro Arcam DAC returned because he did not bring me the hoped-sound improvement of the existing stereo system. I can imagine that for some younger generation who MP3s pieces from Amazon or anywhere else gets online on the Internet, the rPAC gives a lot more sense. But to me

Direct headphone output of rPACs as irrelevant for me, I have not tested.