what have you already done to them? couldnt advise properly without knowing what effects you've already applied to bottom end. if you just boost them you may find yourself with a muddy bottom end and now idea how to clean it up. if you do boost, make sure its b4 any compression. also try a sub kick, your kick sounds nice and punchy but its lacking that real low ooomph.

maybe try a low end boost on the master before final compression.. at least that way all low ends are being upped so should hopefully gel together.

hope this helps