I have always used two subs. Two subs actually augment the size and shape of the soundstage adding much to the width and vertical height. Of the many pairs of subs I have used I have placed them any where from 1.5 inches in front of or at the same plane as the mains. The reason I do this is to align the voice coils of both the mains and the subs so as to more closely match the wavelaunch of both. My hot button for using subs is the net gain in realism of stage not the effect of super deep bass. As you already know the most bass will be at the corner or along the wall,this to me does nothing for the shape or stage of the music. Please make sure you use the coupling devices that came with your speakers and your subs. Direct coupling your speakers will allow you to more quickly dial in the sound placement and all the settings needed to blend your sub or subs into your mains.Tom