For many years, I used my component stereo system to amplify the sound of my Mac. This only requires one specific cable*, and could be accomplished with any kind of audio system [such as one of those bookshelf mini systems or a small boombox] that has an external input. If there's already some type of music system in the room, I recommend going this route.
More recently, I've been using a 3-piece system from Cambridge Soundworks - don'member the model numbah, but it consists of two little 'satellites' [3-inch cubes] and a subwoofer/amplifier unit [approx. 8"x8"x16"] that sits under the desk. Sound is quite clear, detailed, and solid.
I've also used a very inexpensive [20 bux] similar 3-piece system that was quite adequate in its sound reproduction.
* The Mac end of this cable is called a "Mini-Phone Plug" and is the same as those provided on most headphones for the last 20 years or so: it's 1/8" in diameter and has 3 noticeable sections. Traditional component systems will need dual RCA plugs for inputs, while a mini-system or boombox might use either type.
Kb