Hi Guys,
Sorry to arrive at this post so late in the discussion - I see my name has been mentioned already
and I think I have some (hopefully) helpful advice to add....
The top models in the Onkyo range of AV processors/receiver all have RCA pre-out sockets (including the model mentioned above), which make them excellent partners to (almost) all Beolab speakers if you don't have a B&O source or if you want to take advantage of the many sonic and visual benefits that the Onkyo has to offer (read their site for details - there is too much to list here!)
Most Beolab speakers (notable exceptions are the 7.1, 7.2 and 7.4) will accept a Line input which does not need the usual Powerlink switching signals to switch the speaker on. HOWEVER (this bit is important!), the source must be able to control the volume of the line outputs (hence the term "pre-out", ie. volume controlled), otherwise the Beolabs will be at FULL VOLUME all the time (TOO LOUD!) The Onkyo unit has the correct volume-controlled outputs, so is fine to use in this application.
Cable selection is fairly simple for most Beolabs (ie. those with RCA input sockets), as you just need a standard RCA to RCA lead. However, the difficulty is often in sourcing these in a mono version (ie. one plug at each end) in the lengths required for what is basically a speaker cable. RCA leads are usually sold as hifi/AV interconnects in short lengths, so you may have to have them made to order in the lengths required if you can't find the right lengths "off the shelf". Don't panic, there are places who can do this for you at sensible prices.
There are some complications for Beolab speakers with unusual Line input sockets (eg. Beolab 3, 4 and 9), so in these cases you should certainly seek advice to avoid any risk of damaging your speakers by connecting them incorrectly. As mentioned above, the 7.x range of centre speakers are NOT suitable for connection to a non-B&O source (although I'm working on a solution!) 
The Powerlink to Amplifier cables (think I know where you saw them!)
are intended to do the opposite job to the RCA cables I've described above. They plug into a spare Powerlink socket and give you a stereo pre-out to drive a non-B&O amplifier and passive speakers from a B&O system.
Hope this helps,
Steve.
Sounds Heavenly Cables are proud to be a sponsor of the BeoWorld Forum!