As a previous owner of a Beosystem 3 and Beolab 5 I strongly recommend not to rout the audio signal via the Beosystem 3 if you are looking for the best sound. The BS3 does always “something” to the audio signal.
The biggest challenge leaving the Beoworld is volume control if you feed a signal straight to the BL5. There are some work arounds, I ended up with a Core with a optical converterbox and a powerlink connection to the BL5. The TV and the core shared the BL5 Powerlink input via a Almando Powerlink Switch.
Now with my new BL50 much much easier….hope to have my new on order Linn streamer soon.