A little tip for subs, make sure they are in the same plane as the midrange driver/panel. Front or rear firing subs are ok, but down firing subs are not very tuneful.
Agreed upon keeping the sub close to the plane of the speakers but where did you get the idea that down firing is less tuneful. Downfiring front or rear firing will make very little difference to the sound unless the sub is used well above 100 Hz or it has large amounts of harmonic distortion that bleed into the lower midrange (such as on most poor quality subs) - remember bass frequencies propagate in all directions.