Do I need an Amplifier for Component speakers.....?

I have found some component speakers with the tweeters. a href="http://www.tonsdirect.co.uk/component_speakers/alpine/p~SPS-171A.html?cat=44" rel="nofollow"http://www.tonsdirect.co.uk/component…/a . I want to know, because they are 50 watt RMS do I need an amplifier which puts out 50 rms, or would the stereo which also puts out 50 x 4 W do just a good enough job. If I do need an amp, would I need a 4 chan or 2 chan amp? Thanks, Tom.