Exactly. How you wire it depends on the circuit driving the relay - but I assume it will activate the relay when you want the amp on, and deactivate it for off (some circuits work the other way, activating the relay for "off"). In that case, wire the +12 V to the common terminal on the relay, and wire the normally closed one to SMPS J1:1.
Hello Julf - coming back to this thread after a bit of a hiatus. Planning a build this summer, likely using a Ghent audio stereo case. I would use the 12V system trigger (off-state, from the preamp) to close a relay (mechanical or opto-isolator), which then supplies the 5V to the SMPS pin J1:1 and perhaps lights a small yellow LED.
Question for yourself and anyone else that has done this stand-by mode: do you get any transient noises when doing this? Or is the SMPS 'smart' enough to handle power down gracefully? It would be simple enough to use a multi-contact relay to simultaneously ground the nampon pins at the same time, but the fancier you make the plumbing ....
I believe the Ghent chassis uses two Ncore 400 modules and one SMPS 1200; need to verify this.