One option would be to let go of the wireless connections.
With the BL20, you can connect the TV through PowerLink en the Core though optical. The PowerLink connection is higher in the hierarchy than the optical connection, so if you play music through the Core, the TV cannot be set to speaker 2 or 4, only to 1 (so the extra speakers aren't used). When you select speaker 2 or 4 on the Avant, all speakers will be used by the Avant.
I can only assume this goes for the 17 en 19 as well. But you'll loose the wireless.
If I had to do any cables I would prefer to minimize them as my speakers are already mounted on the wall and cables would mean a lot of extra work to hide them.