The "Channels" settings page iTunes tab can have a different value then your main PowerPress settings iTunes tab. Any value left blank in the Channel Settings page essentially tells PowerPress that you want that channel to get its settings from the global PowerPress settings.
So to set custom Channel settings, navigate to PowerPress > Channels page, click the channel you want to edit, then go from tab to tab in that page and make sure all of the settings are filled out. From then on, that Channel will have separate settings from those that are in the PowerPress > Basic Settings page.