The Surround Receiver forms the heart of most Home Theatre systems. The role of Surround Receiver is extensive. It acts as a switching device for all of your incoming sources (Blu-ray, PVR etc) and amplifies these low level signals to a volume capable of driving loudspeakers. It incorporates the necessary Digital-to-Analogue converters, and it is here that the surround processing (Dolby, DTS etc) is done. Many are now connected to your local area network and the internet, by ethernet cable or wifi.
Many Surround Receivers also incorporate additional amplification allowing you to run the system in other parts of your home, independently of your theatre room.
Finally it also incorporates an AM/FM tuner, with some now starting to appear with DAB+ in place of AM, and internet radio via your local network is increasingly popular.