I love great surround-sound for watching movies, but I also use my receiver a lot just for music. The illustration below shows the speaker placement I personally prefer for a 7.1 channel system. The additional pair (over a 5.1 system – for that just ignore the two outermost speakers) are spaced farther out and near the center of the room. This gives a better concert-hall like experience. If you're more into movies most surround sound formats also support placing the last pair higher up in the front for a vertical dimension of sound.
This figure shows the sub-woofer right in front. Some people believe that placing it in a corner of the room at the front strengthens the bass. That makes sense, though I don't hear much difference myself. Again, front placement may be a bit better for music. For home cinema, some people prefer to place the sub-woofer behind the listeners. In fact, a lot of the wireless speaker systems place the two rear speakers plus the woofer in a single enclosure intended to be placed behind the couch.
Don't be too concerned if your room layout prevents you from doing the ideal standard layout. MultiEQ, included in most Denon receivers, does a pretty good job of compensating for different speaker locations. On the other hand, wireless surround speakers can be more flexible if you're trying to avoid long cables.
Surround Sound Setup Test
Running multiEQ is the key part of your surround sound system setup. It's essentially a test, and uses a microphone to “listen” to special sounds sent to the various speakers. Typically speakers are used one at a time and the speakers performance and room acoustics are measured. One of the first things it does is make sure that your speakers are not wired up out of phase (plus and minus reversed on one or more speakers). It may also measure time lags as a way of ascertaining the exact speaker location with respect to the microphone. But if you're willing to spend some time and effort, making some distance measurements with a tape measure will usually give slightly better results.
Notice that the illustration above shows 6 listening positions for placing the microphone during the equalization tests. I'd personally suggest locating the mic at the various locations people are likely to sit while watching a movie. But still keep it close to a regular grid, like in the picture. Actually, I just test with the mic in 3 positions on the couch. My theory is that I get better optimization for just those locations, at the cost of slightly reduced sound quality elsewhere.
Well beyond measured volume and perhaps delay, automatic equalization also adjusts pitch responses (like the old equalizer bar-graph displays and adjustment sliders). This corrects for resonances and other effects of room acoustics. It also measures and compensates for less than ideal speaker responses. That's why I recommend that anyone upgrading to a new receiver go through this setup with their old speakers before deciding whether on not to upgrade their speaker system as well.
Ok, this is on the interwebs so I legally have to show a cat video. Actually it does give you some idea of what the EQ surround test is like. You hear something like noise coming from various directions.
Surround Sound Formats
Beyond 5.1 vs 7.1 channel systems, I found the multitude of different surround-sound encoding formats to be a bit overwhelming. For the most part, I've simply trusted Denon to include all the important ones. But I'll also pass on a few of the things I've learned.
The most common format is Dolby Digital AC-3, a 5.1 channel system. That is 5 speakers plus a sub-woofer. It's what's used on most digital satellite and cable services as well as most DVDs.
Dolby Pro Logic works to artificially create surround-sound from older stereo or 3.1 channel systems. Yes, you can actually get some surround effects out of broadcast TV and even old VHS tapes. Just not as good as AC-3.
DTS is a Dolby competitor's clone of AC-3. DTS-ES brings that from 5.1 to 6.1 channels, while DTS NEO:6 is their answer to Pro Logic. I'm still trying to sort through the newer formats for 7.1, 7.2, and 9.2 channel systems.
At minimum I'd want a receiver with Dolby Digital and Logic Pro. The various DTS formats would be a plus, helping me get surround sound from all the disks and sources I might use.
References: Surround sound technical info.