In turns out that both options have advantages and disadvantages, depending on what source components you are using and what your personal preferences are.
5.1 Channel Home Theater Receiver Overview
5.1 channel home theater receivers have been the standard for two decades. They provide a perfectly good listening experience, especially in small to average-sized rooms. A 5.1 channel system consists of:
1. A Center Channel to provide an anchor stage for dialog or music vocal.
2. Left and Right Front channels to provide the main soundtrack information, or for stereo music reproduction.
3. Left and Right surround channels for side and front to rear motion effects from movie soundtracks and ambient sounds from music recordings.
4. The Subwoofer channel, which provides the extreme low frequency effects, such as explosions or bass response in music performances.
7.1 Channel Home Theater Receiver Overview
However, when trying to decide if a 5.1 or 7.1 channel home theater receiver is right for you, there are several practical features of a 7.1 channel receiver that could be of benefit that you may not have considered.
1. A 7.1 channel system incorporates all the elements of a 5.1 channel system, but instead of combining both surround and rear channel effects into two channels, a 7.1 system splits the surround and rear channel information into four channels. In other words, side sound effects and ambience are directed to left and right surround channels, and the rear sound effects and ambience are directed to two rear or back channels. In this set-up the surround speakers are set to the side of the listening position and the rear or back channels are placed behind the listener.
For a visual look at the difference between a 5.1 channel speaker layout and 7.1 channel speakers layout, check out an excellent diagram provided by Dolby Labs.
The 7.1 channel listening environment can add more depth the surround sound experience, provide more a specific, directed, and immersive soundfield, especially for larger rooms.
2. Although most Blu-ray soundtracks are 5.1, there are an increasing amount of Blu-ray soundtracks that contain 7.1 channel information - whether it be 7.1 channel uncompressed PCM, Dolby TrueHD, or DTS-HD Master Audio. If you have a 7.1 channel receiver with audio input and processing capability via HDMI connections (not pass-through only connections), you can take advantage of some, or all, of these audio capabilities. Check the specifications, or user manual, for each 7.1 channel receiver you may be considering for more specifics on its HDMI capabilities.
3. Also, even with playback of standard DVDs, if your DVD soundtrack only contains Dolby Digital or DTS 5.1 or, in some cases, DTS-ES 6.1 or Dolby Surround EX 6.1 soundtracks, by using the Dolby Pro Logic IIx extension or other available 7.1 DSP surround modes that may be available on your receiver, you can still extract a 7.1 channel surround field from both 2 or 5.1 channel source material.
4. Other surround sound extensions that can utilize 7.1 channels are Dolby Pro Logic IIz and Audyssey DSX. However, instead of adding two surround back speakers, Dolby Pro Logic IIz and Audyssey DSX allow the addition of two front height speakers. This provides additional speaker setup flexibility.
5. In addition, if you prefer 5.1 channels for your main room, most 7.1 channel receivers have the ability to use the extra two channels to provide a 2-channel speaker operation in a second location. What this means is that, in many cases, while you are listening and watching your DVDs in 5.1 channel surround sound in your main room, someone else could be listening to a CD (provided you have a separate CD player connected to your receiver) in another room, without having a separate CD player and receiver in the other room - just the speakers.
6. Another option that is becoming more common on 7.1 channel receivers is the use of Bi-amping. How this works is that if you have front channel Speakers that have separate speaker connections for the midrange/tweeters and the woofers (I am not referring to the subwoofer, but the woofers in your front speakers), you can reassign the amplifiers running the 6th and 7th channels to your front channels. Then enables you to retain a full 5.1 channel setup, but still add two additional channels of amplification to your front left and right speakers.
Using the separate speakers connections for the 6th and 7th channel on your bi-ampible speakers, you can double the power delivered to your front left and right channels. Your front mid-range/tweeters end up running off of the main L/R channels and your front speakers woofers running off your 6th and 7th channel Bi-amp connections.
The procedure for this type of setup is explained and illustrated in the user manuals for many 7.1 channel receivers. However, as I mentioned earlier, although this is becoming a more common feature, but is not included in all 7.1 channel receivers.
9.1 Channels and Beyond
As more sophisticated surround sound processing options become available, such as DTS Neo:X, that can expand the number of channels that can be reproduced or extracted from source content, manufacturers are upping the ante on the number of channels they can cram into a home theater receiver chassis. When moving into the high-end home theater receiver arena, there are an increasing number of receivers that now offer 9.1/9.2 and a small number that even offer 11.1/11/2 channel configuration options.
However, just as with 7.1 channel receivers, it depends on what you want to accomplish in your home theater setup. Both 9 and 11 channel receivers can be used to set up 9 or 11 speakers (plus one or two subwoofers) in your home theater room. This allows you to take advantage of surround sound processing systems, such as DTS Neo:X. However, a 9 or 11 channel receiver can also provide flexibility in terms of assigning two of the channels to Bi-Amp the front speakers, or using 2 or 4 channels to create 2nd and/or 3rd Zone two channel systems that can still be powered and controlled by the main receiver. This can still leave you with 5.1 or 7.1 channels to use in your main home theater room.
Keep in mind that the vast majority of DVD, Blu-ray, and any surround sound audio that you will receive from source content is mixed for 5.1 channel playback, with a smaller number of source content mixed for 6.1 or 7.1 channel playback. This means that a 5.1 or 7.1 channel receiver with Dolby/DTS decoding and processing can easily fill the bill (A 5.1 channel receiver can place a 6.1 or 7.1 channel source within a 5.1 channel environment). When moving up to a 9.1 or 11.1 channel receiver, the receiver is actually post-processing the original 5.1, 6.1, or 7.1 channel encoded soundtracks and placing them in a 9 or 11 channel environment. The results can be quite impressive, depending on the quality of the source material, but it does not mean that it is required that you make this leap. After all, many don't have the room for all those extra speakers!
To put it all into perspective, a good 5.1 channel receiver is a perfectly fine option, especially for a small or average room in most apartments and homes.
However, once you get into the $500 range and up, there is an increasing emphasis by manufacturers with 7.1 channel equipped receivers. Additionally, when you get into the $1,300 an up price range you start seeing some 9.1 channel receivers. These receivers can provide very flexible setup options as you expand your system's needs, or have a large home theater room.
On the other hand, even if you don't need to use the full 7.1 (or 9.1) channel capability in your home theater setup, these receivers can easily be used in a 5.1 channel-only system. This frees up the remaining two or four channels on some receivers for Bi-amping use, or to run one or more two-channel stereo 2nd Zone systems.
For additional information on home theater receivers, check out my related articles:
Also for an additional perspective, check out an article from About.com Stereos: How Many Channels Do You Need?