check the resistance that the subs can take,not all can take halving the resistance (ie 2 ohms) and this could cause a fire in ur car! if they are able to take a 2 ohm resistance then this will obviously make it louder but otherwise just use the speakers as one per channel.
with regards to your front speakers id seriously look into getting either a smaller amp or bigger speakers (from ebay or last years demo stuff from halfords etc...) as they are totally mismatched!the amp is kicking out twice as much power at the rms level as the speakers can give out,remember rms is what u should ideally look at,peak power is utter horse shit and means very little (its what they spike to occasionally),speakers can be cheap to get hold of so browse around,itll save you a lot of heartache,i promise! or....get yourself some 6x9s and run them off the amp (again get them paired up nicely) and run the alpines off the headunit as they seem pretty close to head unit outputs
are u just looking at massive noise or some clarity?