The line-in of the Playmaker has 'autosense' - which means that it will turn on right away, when the BeoGram (or whatever is connected) is started.
Just be sure that AirPlay/DLNA is not still activated from a former playback.
That is how it works in my setup for years now.
Start your BS9000 as you already do it - with A.MEM - but be sure, that your Playmaker is set to Option 0.Otherweise that would receive the ir-commands as well (A.MEM would initiate AirPlay there).
The volume output of the Playmaker should be set to 'fixed' - and all volume should be controlled via BS9000/Beo4.
MM
That's exactly how my PM and BS9000 are set up. I have a Beogram 3000 tangential run through an outboard phono preamp and into the aux in of the PM, and the PM hooked into my BS9000 aux/tape input. Option and volume set as you say above. Works perfectly, but if you start a wireless playback source, Airplay or DLNA, it takes precedent over the phono/aux input as mentioned.