Beolab 5: Sync cable necessary when using BS9000 as CD Player with SPDIF

Prior to the purchase of a pair of beolab 5 i am currently planning the setup. Since i don´t need a TV in the living/listening room i will probably go for a network player. I know that the sync cable is used to keep the same volume level on both speakers, when for example the IR signal of the Beo4 only reaches one of them. In the manual, there is mentioned many times, that when using a B&O System, you don´t need the Sync cable. 

Does the Digital Out of the Beosound 9000 have a "built in" volume sync or would you need a Sync cable in any case of a digital input, B&O or otherwise?

I don´t really get the difference between having the B&O CD Player or any 3rd party (CD or network) player with a SPDIF output. My guess is, that the only way to get rid of the sync cable would be using powerlink cables, yet unnecessarily bloating the setup by having my network player (digital) plugged into a BS9000 (analog) when i have speakers with a decent DAC built in.

My aim is to simplify my setup - i just want the two speakers and a silent player to stream spotify, tidal or my local files (i digitized all my CDs, to get the BS9000 out of the room). So just hook up the RCA cable and a Sync cable, right?

And isnt the digital out of the Beosound 9000 ONLY the CD signal? So you couldn´t even connect the BS9000 digitally to the Beolab 5 when you wanted to plug a 2nd source into the Aux-In of the BS9000.

I am aware of the option settings that need to be adjusted in this case.

Don’t know if you have this manual and whether it goes a way to answer your question:

https://www.manualslib.com/manual/213520/Bang-And-Olufsen-Beolab-5.html