A quick answer is yes there is a difference between Surround speakers and Stereo Speakers, how ever stereo pair speakers can be used for surround sound.

    Surround speakers can come in a package and they are all alike, and we refer to it saying Matched speakers. What do we mean by Matched ? We mean they are all similar. So when you have a 5.1 surround speaker system, you have a matched 5 speakers, and a sub woofer. No matter how these speakers are designed. They can be Satellite speakers and a sub woofer, or Tower Speakers, or Book Shelf size, or even Floor Standing types.

Stereo Speakers :

    When using stereo speakers, people tend to buy two huge floor standing speakers, and they address it as Main speakers, and we often choose them with high power specifications and from a good company. As much as you invest in main speakers as much as the sound details you will enjoy.

    Main speakers can be used with a surround system too, they are set as front speakers, Front/Main speakers carry out the sound effects, and the music or the theme of the movie. To enjoy a good front imaging system a matched center speaker, or a center speaker made by the same manufacturing of your main speakers, should be added to your system. This will create good harmony and the sounds will not differ from a channel to another.

    Example:  If there is an effect on the front left channel, and it moves to the center and continues to appear in the front right channel, you wouldn’t realize any change in the type of sounds, you will just feel the movement of the sound and thats what exactly needed.

    It would be very bad, if an actor was talking and his voice is coming from the front right, then it came from the center and you felt that his sound did differ. This is an undesired thing to happen.

Surround Speakers :

    Choosing a matched speaker set from the beginning can save you many problems, and when the speakers are positioned in their correct places, all what you should think about is the equalization due to room acoustics. If the speakers are not similar, it would be very difficult to make accurate equalization.

Combining Speakers with different sizes :

    Combinations of speakers with different sizes can be used together, and for each combination, a setup can be made with the surround amplifier used.

    When the speaker is of a large size, it can produce low frequencies like bass, hence narrowing the frequencies sent to the subwoofer and the frequencies sent to the main speakers itself is widen.

    The surround sound processor is the unit responsible for sending the correct frequency and data to each channel. It sends the full  frequency to the main speakers, in case they are large, and send only the LFE to the subwoofer. And if the front speakers are small it does not send all of the bass to the front speakers, however it sends the bass to the subwoofer with the LFE signals too.