Getting Surround Sound – The Home Theater, AV, or Surround Surround Receiver
To get surround sound, you need a component that can decode and reproduce surround sound from a source, such as a DVD. Most commonly, this component is referred to as an AV Receiver (Audio/Video Receiver), Home Theater Receiver, or Surround Sound Receiver.
A Home Theater, AV, or Surround Sound Receiver usually combines the functions of three components:
1. A radio tuner for AM/FM and, in some cases, HD (High Definition Radio) or XM-Satellite Radio.
2. A Preamplifier that switches and controls which audio and video source is selected (such as a DVD player, VCR, CD player, etc…) and processes the incoming stereo or surround sound signals and distributes them to the correct amplifier channels and the subwoofer output. The preamp in an AV receiver can also route video signals coming from source components (such as a DVD player) and direct the video signal to the television.
3. A built-in Multi-channel amplifier (5.1, 6.1, or 7.1 channels) that sends the surround sound signals and power to the speaker system.
Receiver or Separate Components
The Home Theater receiver is the heart of a home theater system and provides most, if not all, the inputs and outputs that you connect everything, including your television, into. An AV Receiver provides an easy and cost-effective way of centralizing your your home theater system.
However, in many higher-end installations, the functions of a Receiver are often provided by separate components: Preamp/Processor, Tuner, and either a single multi-channel amplifier or even separate amplifiers for each channel. Such a setup provides more flexibility in switching out and/or upgrading the separate aspects of the system as well as isolating any interference that is caused by having all these functions combined in a signal chassis and sharing the same power supply. For the average consumer, however, a good Home Theater, AV, or Surround Sound Receiver will function just fine.
Source : about.com