I have a powerful computer running Linux (Debian) desktop. I use it for work as well as for night-time computations. So it's running 24x7. I also have non-smart TV with HDMI input and dedicated Pioneer receiver for sound. What I want is to use my computer as a media server. I do not want to connect TV as a second monitor because it will interfere with my work. I want some application that will run in background, stream content directly to HDMI and digital audio and be operated by some client. I have looked at the Kodi but didn't find out how to run it in background and how to dedicate HDMI port to it. I have looked at Plex but it requires Plex Client App on output device. I could buy something like Chromecast as a last resort but I will be not able to connect my audio receiver then.
Are there any options to achieve what I want?