I am putting in an pioneer head unit putting out 15 watts rms per chanel. In the front i am putting in 4x6 pioneers rated up to 20 watts rms. So that works out fine. How ever in the back I want to put in alpine type r 6x9s. They are rated up to 100 watts rms. Can i run them with just the head unit or is that to underpowered for thee type r speakers.

 

Run em with the headunit just fine, just use the fader to fade to the back a couple of levels so it sounds even all around.

 

What you are doing will work but you will suffer in quality if you want to turn the volume up (And I dont mean cranked). Deck power will never give you really clean, undistorted sound. It would be money well spent to buy a $100-$150 amp and have a shop install it--Your sound quality will improve 100%.