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

if u are just replacing ur stock speakers in you car with new and better speakers then no u will do just fine with the built in amp in your radio... however adding a 4 channel amp for you componets is never a bad idea.. it will put them to there full potential and will sound alot better

That 50 x 4 W for the receiver is most likely a meaningless peak power figure. Most decent aftermarket units put out somewhere between about 18-22 watts RMS. If the receiver is also an Alpine, you might consider adding the Alpine Head Unit Power Pack, KTP-445, which is a "plug-and-play" amplifier and boosts the RMS power to 45 watts. If you want to boost just the power to the Alpine components, a 2-channel is all you need. In fact, if the rear speakers are OEM stock, their power handling capability is probably exceeded by most aftermarket head units and adding an amp to drive them would be overkill.

You can use an after market head unit to power them, they are not that different than two way speakers only with a separate cross over...and they will sound better too. check out what the effency rating is 84db would be low 97db would be high the higher the number the louder they will play with minimum power.

No point in powering them with your head unit, just get coaxials. Compnents usually crave an amplifer, they dont come to their full potential without an amp. Your head unit is really more like 20 watts if that. Trust me, you will not regret getting an amp. It might sound ok off the head unit, but wont get as loud as you probably want.