That amp is a mono amp and def is more then enough for the sub lol. You mentioned about a 4 channel amp did you have one or was thinking of purchasing one? In the end it sounds like your worried the 8 in is not going to give you enough bass hence why you want to do the earthquakes. Personally I would do this. Since you have the sub and amp hook it up and see what kind of bass you get. If you are happy with it then just go component route. Then hook up the comments to the headhunt and see how they sound if your not happy with the sound then you can get a 4 channel or a 5 channel amp and power everything. If the 8 is not enough bass and you decide to get 6.5 earthquakes then keep in mind the headhunt will not be able to power it and you will need wire an amp to them. You might be able to where the earth quakes with the pioneer but not sure if i would recommend it. Also if you end up adding more amps i would def upgrade your wire to a bigger gauge like 4. Bigger wires take more strain of your amp cause it does not have to work as hard to gain power. hope this helps