Marantz NR1200 with Emotiva BasX A-300

Glad to help.  

Enjoy.

I don't see either a 12V trigger in or out on th e NR1200, so you don't have a direct method.  There might be work around.  You might be able to use two smart outlets and turn both on with a programmed routine.  (i.e. with Amazon Alexa outlets... create routines for "Stereo On" and "Stereo Off".)  The key is if the power buttons for NR1200 and A-300 are a hard on/off or soft buttons.  If they are hard on/off, it would work.

Just an idea.

You can, but you still need to have something to trigger/turn on the power from that eBay power supply.  The key is still the power button on the Marantz.  If it is a hard on/off (i.e. if you turn the Marantz on and then disconnect the power, when you reconnect the power the Marantz comes back on) then you could us the "smart outlets" or plug the Marantz and the 12V wall wart into a power strip and use the on/off button on the power strip to control it.

Yes.  The Emotiva should turn on with using the powerstrip configuration with the 12V power adapter.