Sonarr is definitely brilliant for this, but it’s best with a Usenet account. You can customise your preferences so it will only download x265 with 5.1 audio at a given bitrate, for example, and this can be set on a per series basis if you want. It’ll also download any new episodes that are posted automatically and move them into your media folder, depending on how you set it up. It works best for more recent shows, older series tend to be a bit spotty due to takedowns.