Spare channel = sq?

I have a 2 channel amp driving my rear speakers, 1 monoblock sub amp 3 channel (with the 3rd 150w mono channel doing nothing) doing the fronts. Question, is it worth putting a small 8inch sub on the spare channel to help the mid bass transition or will it cause too much of a peak? Sound Quality is my goal. At the moment I'm not too inpressed with my front speaker mid bass output because of their install rather than the speakers themselves. (dimaond hex 6.5's)What's that flippie??

It would be worth experimenting with it if you can get the mid-sub up front and center.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.