As already mentioned.
The beoport doesn't have a internal DAC. Therefore the quality depends on the attached source, the soundcard of the pc.
It can be improved to install a better soundcard in the pc or to invest in an external DAC (like the DACmagic).
Another point is that the quality of the output on a pc/mac depends on the attached device. The internal impedance of a headphone differs from a input from the beoport. That can make the difference in sound.
So a special soundcard with special line -out, will give a better result than a iPhone/Pad or other source wich is designed for headphones.
Of course, the shorter the route, the better the quality might be.
I assume that the used switching technology on the beoport board should be on the same level as used on the av-boards in all the Beovisions.