Select multiroom receivers remotely

[abrakadabra2k]

Hi all,
I have a working multiroom setup with 3 receivers. But rarely all three are active. Currently I do this manually via GUI checkboxes:

I would like to change this settings via http requests (like http://IP/command/?cmd=). 
I searched through the setup.txt and mpd protocol, but could find nothing that helped me.
Can someone point me in the right direction?
Alternativly to activate/deactivte a receiver I could also live with muting it, if this is easier

[Tim Curtis]

Whats the usage scenario where its not possible to use the WebUI ?

[abrakadabra2k]

I want top integrate it in my Alexa (as Seen in https://moodeaudio.org/forum/showthread.php?tid=4771 )

[Tim Curtis]

Have a look in /var/www/scripts-panels.js for the comment

// Multiroom Receiver control

[abrakadabra2k]

Thanks, Tim.
Back than I didnt find the time to research more. 
Nowadays it seems fairly easy as it is a not yet documented http command:
http://<Receiver-IP>/command/?cmd=trx_control%20-rx%20On
http://<Receiver-IP>/command/?cmd=trx_control%20-rx%20Off

Finally i can do it via a quick voice command