Without getting too technical, the higher the wattage rating of a set of speakers, the louder and clearer the sound will be. Remember, though, that the wattage quoted to you by the manufacturer is the total wattage output of all the speakers combined.
Suppose you have two sets of speakers you are considering buying, a 5.1 and a 7.1 system. Suppose that the total wattage of both systems is 400 watts and both have a subwoofer with 50 watts of power. That means that both systems have a 350-watt power rating for the directional speakers.
However, since the 5.1 system has 5 directional speakers and the 7.1 system has 7 directional speakers, the individual speakers in each system has a different average rating. The 5.1 system has an average of 70 watts per speaker and the 7.1 system has only 50 watts of power per speaker on average. This is not such an important consideration for high-watt systems such as the example above, but for lower wattage systems, it can mean the difference between clear and tinny sound. Remember to do the math or look carefully at the individual power ratings of each speaker in any system you are considering purchasing.
Headphones operate on much the same level as speakers. To get the best sound from a set of headphones, pay close attention to the Power Handling Capacity rating. Anything in the 1,000mW to 3,000mW range could be considered “studio quality” and capable of delivering true-to-life sound.
In the case of headphones, you get what you pay for. Plan to spend about $100 to $400 for entry-level DJ style headphones. Anything less and you risk tinny sound with little bass. Of course, some headphones reach into the $800-$1500 range. Unless you are a professional mixer or DJ, you probably will not get much more quality out of such an expensive set of headphones than you would with entry-level systems.