question about my amp and speakers

So I have 4 cabin 6.5 speakers, 2 are rockford and the other 2 are kickers, neither are the highest end speaker but i think mid to upper for each brand, i have two 6x9 polk momo tower speakers as well. I have a 4 channel diamond audio amp 400 watts and the rockfords and polks are running to each channel and the kickers off of my HU. Would it be okay to run the kicker off of the amp as well? And what would be the best way to wire them, directly to the amp in the same outlet as the rockfords, or wire them speaker to speaker then the amp? I have the gain turned 1/4 way up on the rockfords and about 2/3 on the polk tower speakers.