SiriusXM is a satellite/internet radio company, which has offered an Android smartphone app since 2010. The company has also embraced Android’s other form factors – a Google TV app is still live on the Play Store. An Android TV version is now widely available, with seemingly no announcement from the company.
The app is already up to version 1.1, and since the changelog says “Added support for more Android TV devices,” it may have only been available on select smart TVs. You should now be able to download it on any set-top box or smart TV running Android TV. At the very least, my Nexus Player shows up as compatible.