IIRC, (50:50) the BV10 has only an SPDif Input. No audio digital ouptput. Thus, the BL5s can only be fed via powerlink.
If you are using the BV10 as a Master and have say a BeoSound5 in the setup via Masterlink, then you can connect the BS5 SPdif output to the BL5. However, you will still need to connect the powerlink from the BV10 to BS5 for volume control.
I was never convinced, but you can also continue the SPDif/Coax out of the BL5 to the BV10 SPDif input in a closed loop. This in theory should give optimal sound from the BS5/BV10 if you choose (for any bizarre reason) through the centre channel.
As above. 50:50. You may want to ask a friend for an alternative answer.