If you can stream or cast it through another App, or the App you are currently using to the TV, then SoundSend will play it.
Most smart TVs have applications for the same services you use on your phone like Spotify, YouTube, Pandora etc. For instance, in Spotify you can connect to your smart TV and cast whatever you are playing on your mobile device account to it. Once connected you can control what's playing from your phone, but the SoundSend will be playing the music from your TV output. This is a scenario where SoundSend will work through your TV with your mobile device.