CDJ switching receiver inputs

I've connected these components to my v2.0 Slink-e:

Receiver: STR-DA50ES to S-link port 0

CD Changer: CDP-CX555ES to S-link port 1 & Receiver's "CD" input

CD Changer: CDP-CX333ES to Receiver's Control-A1 & Receiver's "MD/DAT" input

Things kind of work but I've got a couple of questions I haven't been able to figure out:

Is it possible, using the Control-A1 buss (rather than IR), to control my receiver from my PC? Specifically I want to be able to double-click on a disc or track in CDJ and have the receiver automatically switch to the correct input. How would I do this?

Am I supposed to be able to use my receiver's 2-way remote normally with everything connected via Control-A1? It seems like I remember Sony telling me to disconnect the buss to get the remote to work properly (album IDs, etc.)

What's the CPU upgrade about?

Thanks,