although you could use a 4 channel amp, i would use 2x 2channel amps, that way each amp could have the gain set correctly for each set of speakers, a 250w rms 2 channel would be fine for the 6x9, and mabey a 300w or 400w rms 2 channel for the subs (or a monoblock, with the subs parallell - if the amp could cope)
if you used a 4 channel that didnt have seperate gain controls for the channels you would risk blowing up the 6x9s trying to get more from the subs (this can be corrected through the head unit to a certain degree, but all it takes is a mate to piss about with your headunit whilst your out the car, and pop goes the 6x9s)
as for specific recommendations, i dont like to make any as I sell amps and speakers and could be seen as biased so i prefer to explain how they work, then let customers make there own choice. reading reviews on amps etc on forums like this or elsewhere on the 'net is a good way of finding out whats hot and whats not.
