JD, welcome. Yes, a four speaker setup with side surrounds(probably best a couple feet farther back than directly to the side)would be good for both music and movies. Using processing such as DPLII or Logic 7, depending on what your receiver has, the ambience present(to varying degrees)in two channel material, which originally came from the sides or back, is extracted from the front channels and directed to the surrounds where it belongs and makes the listening experience a bit more realistic.
For movies the two main speakers can form a "phantom" center in the absence of an actual center speaker. The .1 LFE channel occasionally present in movies for special effects would be directed to the mains if a sub wasn't used, as would be the low bass from the surrounds set "small".
