I know, RPi has not Standby or suspend mode, but I use some commands to save power. Maybe you could embed such a function.
It would be nice to have the posibility to suspend with a Hardware-Trigger over GPIO which shut down not nessercary processes, ports, and also sends another GPIO Signal where a relais could be triggered to shut down an amp. Optionally it should be possible to configure, which services are suspended, i.e. Bluetooth/Wifi/Ethernet/USB-Power/amp over GPIO/…
rpi3 + 7" Touchdisplay with speakers ~8W even when not playing and Display is black (backlit is still on)
sudo /opt/vc/bin/tvservice -o
sudo echo 0 | sudo tee /sys/class/leds/led1/brightness
sudo echo mmc0 | sudo tee /sys/class/leds/led0/trigger
sudo echo 0x0 > /sys/devices/platform/soc/3f980000.usb/buspower
sudo cpufreq-set -g powersave
Now the pi only consumes 1.4W-1.6W
To wakeup I reverse the settings to normal.
I think, you know even more options to save power.