Hi Francisco - and welcome to the community.
Happy to try and get you set up here.
The extension you need to look for in Extension Manager is under “Device Control” - Extension “Rheos”.
Make sure you are folllwing the instructions to use the latest Extension Manager Version 1.1.2 Roon Extension Manager 1.x (currently at v1.1.2)
Select “Download and” then “Start”.
The “Denon/Marantz AVR” is much older and doesn’t use UPnP/HEOS at all.
The RHEOS extension attempts to better integrate HEOS with ROON and allow high quality streaming and the ability to control HEOS groups from the ROON interface.
Let me know how you get on - once you find the correct extension. This is still in Beta so any feedback will be greatly appreciated and I will try to help you with installation etc.
Best regards,
Peter