Home theatre system can be brought in separated components or all in one package. But buying in individual components is much prefer as you can get the best of all the systems. In home theatre speaker system you needs a good audio systems, you will needs a midrange speakers, a subwoofer, a set of tweeters and how many speakers you needs to install to get the best surrounding sound for your home theatre.
The most recommented sound surrounding systems are Dolby Pro Logic and Virtual Dolby.
A good crossover can make any driver sound good, while bad crossover can make even a good driver sound bad. The room surrounding also play a big role to the sound systems.