Essential for "immersive" audio. A 5.1.2 setup, for example, uses five base speakers, one sub, and two height or ceiling speakers to create a 3D sound environment.
Ideal for small to medium rooms. It includes five speakers (Front L/R, Center, Surround L/R) and one or two subwoofers. home av receiver buying guide
Best for larger spaces. It adds two rear surround speakers to the 5.1 setup to fill the room more effectively. Essential for "immersive" audio