When purchasing a home theater system you will want to look at its power capabilities. For your den, dedicated to home theater, you may want to look at a receiver with 80 watts. If you are going to be doing your theater going in your bedroom, 40 watts to 80 watts may be adequate.
The terms DTS and Dolby can be confusing. For the home theater system, DTS-DS stands for Digital Theater System Digital Surround. Many DVD players will support DTS 5.1 and 6.1 channels. It is the least compressed audio and therefore, some say, a better option. Dolby Digital is another technology for coding and compressing sound. The Dolby Digital 5.1 has 6 channels of sound (the left and right front speakers, the left and right back speakers and a subwoofer.) It is the HDTV industry standard at this point. Knock it up another level and you are talking Dolby Digital Surround EX, or 6.1. The Star Wars production company, Lucasfilm helped develop this technology.
You may also hear the term THX, which also has ties to Lucasfilm. In home theater systems, it refers to the fact that the device has met particular standards in audio/video. It is compatible with both Dolby and DTS and is an assurance that you will be getting industry standard sound.
Most systems will be Dolby Digital, as are the general DVD population. Keep in mind if you intend to actually listen to dialogue while watching your movies, that sound comes from the center channel speaker, so pay particular attention to that when trying out your system in the store or at home.
But watch out
Keep in mind this is not top of the line equipment. The speakers offered in these systems are not the highest quality. If you pride yourself on your ear for sound, you may want to shop for separate units and speakers that will meet the standards of your discriminating ear. In fact, if you intend to listen mostly to music on the system rather than the audio track of a movie, you may be disappointed as the audio on home theater systems are designed specifically for the home theater, rather than the delicacy of Handel. But with today's technology, these lower end speakers can sound very, very good.
If you intend to upgrade speakers, know that most of the home theater in a box systems have proprietary connections that do not allow for speaker swapping. This can be a problem is the speakers are low performers.
If you are media heavy, and intend to hook up your video game console and your digital satellite TV and your VCR and your CD player...make sure the system has enough audio video outlets to satisfy your home theater needs.