Sorry if this question seems to be a repeat of others before me. I have just bought a set of Infinity 6000CS component's (90 RMS) for the front of my SUV and a set of Infinity 6002I 2-ways (60W RMS) for the rear. I currently have an Alpine CDA-9831 HU and run two 10 inch subs in a band pass box with a 2 channel, 400 Watt amp. Am I crazy to simply install the new speakers powered off the HU? Will the speakers sound bad or be in danger of clipping damage if I dont use an amp? If I amplify them, do I need to do all 4 speakers or just the front? And what size of amp is recommended?
if it were me, i'd power the front speakers with an amp and drive the rears with the head unit. infinity makes a new series of reference amplifiers, one i think is rated 97 Wrms x 2. it's pretty affordable and small in size; nice-looking, too.
if you'd rather, you could get a 4-channel amp, but turning up the rears really doesn't improve the sound that much. i think it's waste of resources to amp the rear fill.
as far as damaging your speakers, i wouldn't worry about it. the biggest problem driving your fronts off the head is a lack of dynamics. basically, your music can't get loud enough to sound good because the head will clip and distort on loud bursts. this ends up sounding bad when you turn it up, or when the bass hits pretty good.
with an amp, you can enjoy those dynamics and better use the capabilities of your components. you'll notice clearer sound, louder sound, and punchier bass response.