external amp?

 I bought a pair of Infinity Kappa 3 way 6x9s. I was going to put them in the place of my old blown factory speakers the other day but i went up to the local car audio store and the guy told me that if i install these speakers i should use an external amp to give it more power since my head unit is a 45x4 premier pioneer.   I guess it won't give the speakers enough power and my brand new 6x 9's will blow because according to him "infinity kappa need as much power as possible because they are the top of the line".  i was terrified by this and I don't know what amp i should buy to power my speakers. If anyone could give me a few names of amps that will sound the best and work the best on my 2 new speakers i would greatly apreciate it!

It doesn’t matter if there the top of the line or bottom of the line speakers if you run them at a normal volume they will not blow. Your head unit probably puts out 20 watts x4 rms. There is some truth to what he was saying what blows speakers is distortion and when you push your head unit at very high volumes it puts out distortion which blows speakers. My advice to you would be if you’re not turning the volume control up then don’t get an amp.  But if you want louder music and want to be able to push those speakers then get an amp.