More than just an amplifier, a home-theatre receiver is the core of a home-entertainment system. It ties everything together, so that you can watch a movie, play a game and even gain access to internet media.
The excellent Yamaha RX-A2010
But the fundamental job of a home-theatre receiver is really to amplify your loudspeakers. A surround-sound system has five or more loudspeakers, with the industry settling on seven as the norm, so most receivers have seven amplifiers — although the Yamaha Aventage RX-A2010 and the Pioneer SC-LX85 trump that, with nine amps.
The receivers below decode all current digital-audio standards, including Dolby Digital, DTS, DTS-HD Master Audio and Dolby TrueHD. All must have inputs and outputs for the devices you will be connecting to them. Most important is HDMI, but if you have some older source device with S-Video output, be careful; a lot of manufacturers are dropping this.
If you are planning a home-theatre system with a projector, then a receiver with two HDMI outputs can be important. That way, you can also have a regular TV plugged in for everyday viewing, without having to rewire for the big-screen movie on a Saturday night.
Being "receivers", they all have AM/FM tuners built in.
All of the receivers below move beyond the traditional home theatre by providing support for networking and USB. Both are for media playback, mostly audio, although some of them make a laughably bad attempt at rendering photos, too. The networking is best employed for extracting music from your home network via DLNA, and for dialling up some of the tens of thousands of internet radio stations.
Some allow network-aware mobile devices to push music to them: AirPlay for some models, which has now become a bit of a default, along with DLNA for the newer receivers.
In the last couple of years, receivers have had to cope with yet another new video standard: the frame-packed format for 3D (equivalent to 48fps). With it came a feature called Audio Return Channel (ARC). This allows the HDMI cable that takes the picture from the receiver to the TV to double as a digital-audio cable, taking sound from the TV back to the receiver. When you're watching a TV broadcast, you can then have surround sound from your home-theatre system.
These receivers can also take analog video inputs and turn them into HDMI. The idea is that you then need only one neat cable from receiver to TV. Some of them also have pretty classy up-scaling (if you choose) for all inputs, but this is far from vital.