Dolby Surround Pro Logic: This multi-channel format can also be played on regular stereo equipment. In addition to the right and left, there is also a surroundChannel, which is limited from 100 Hz to 7 kHz and is sent to the rear speakers in mono. Since the surroundSignal from the two stereochannels is extracted, the surround effect is weak. Many TV movies are broadcast in this format, which has been around since 1987.
Dolby Prologic requires rear speakers that cannot be located. You can point them against the back wall to get additional reflections. They transmit a narrow frequency band and both are fed with the same signal. So it's not a problem to use "humble" things.
The Dolby Digital or discrete 5.1, 5 equivalent channels are available. This means that ALL 5 channels are equipped with the same loudspeakers. Only in an emergency, when there is an extreme lack of space, is a smaller version of the same loudspeaker used. In the studio, for example, 3x Genelec 1032, 2x 1030.