I have a similar cofiguration, from the Airport Express to a Beosound Ouverture. It works fine, except for the sound quality. The Airport's digital/analog (D/A) converter obviously doesn't live up to B&O quality.
Fortunately, Airport Express realizes its weakness and offers digital output as well, through the same contact. You buy a separate D/A converter and connect it between the Airport Express and the Beosound.
For me a separate D/A converter is on my wish list. I investigated it some time ago and found that they have not reached the mainstream consumer marked yet. Consequently they are rather expensive so I dropped, no, postponed, the idea.
Does anyone have some recommendations for D/A converters?
Sigmund