They're at PM6007 already? I'm still at PM6005 lol.
Anyway... there is no difference between these inputs. CD/network/tuner/tape... all of them are electrically identical and are only named that way so that when your friends come over and look at the front of the amp or in this case the remote control, they know what button to press to connect to the tape recorder for example. The only exception is phono for obvious reasons.
I can't remember when I was told this, but if you have nothing else to connect to and your main connection is not listed, you should connect it to CD. I guess it is kind of an unspoken practice that allows people to find the "default" audio source quickly? I try to do that but I settle for the first one that the cable reaches.
I guess RPi4 can be classified under "network"...