installed new pioneer head unit w/ alpine speakers... need help Options

[DIONYZUZ]

So I just installed the pioneer head unit that supports 50w per speaker and I got 4 alpine type r speakers that support a peak 600w per pair (1200w total) . And I hooked the unit up connected to the factory amp, which I'm thinking was not such a good idea. When I installed they two front speakers they sounded decent, but it seems like the rear speakers are barely letting sound out. At first I was thinking it was the speakers, but now I think the amp to the unit is distorting the signal for the speakers. Would it be better for me to replace the factory amp with a pioneer amp to get these alpines with better power and clarity or is the factory amp not a problem?

[DIONYZUZ]

Yea... I ended up ordering a 4 channel pioneer amp witha max of 760 watts to match with the pioneer head unit. I was wondering why the original wire harness did not fit, because its connected to the amp. I got the harness that connects from the amp to the original head unit and I spliced it from there so I was able to use the coaxial input for the speakers into the pioneer head unit. It cost $30 from autozone >.< which was a waste of $$ so I dont feel like buying another harness... eBays got them for waaayyy cheaper and is well worth the wait. I found the correct settings for the rear speakers which were originally set to be subwoofers and found that one of the speakers was a defect from the factory so I sent it to be replaced. The speakers actually worked pretty well with the factory amp, but I will soon be getting that 4 channel amp for $130 from eBay Pioneer 6500F 4 Channel.