Hi Koert,
the port named PC is not a PowerLink-port.
You need an adapter for (PC)DIN/male to Phono/male - ask your B&O-dealer for details.
You might also consider using a small DAC (for the digital-out of the APE), because the analog-out is not the best. That is, if you want the best-possible-sound :-)
!!! The Active Link - OF COURCE - has to be in a MasterLink-chain !!!
If you could find your BS9000, you might instead connect the APE to the AUX of the BS900 - and set up the BL Active as usual with your BL's in the room you choose for it. That way you can listen to AirPlay-sound in different rooms.
See my solution with the Playmaker here:
www.hifi4all.dk/forum/forum_posts.asp?TID=46053&KW=millemis&PN=0&TPN=235
It is in danish, but you can let Google translate and atill "get the picture".
And feel free to let you inspire ;-)
P.S. If you only want the APE and the BL's, you might connect the analog-out of the APE direct to the PL-in of the BL4000 (set to line).
And adjust the volume on your iDevice/Mac or iTunes/Pc.
Not the best solution, but it will work.
Greetings Millemissen