Always makes me laugh when size is the issue. Especially when it's so close. The average mans hand from below palm to middle finger is 7.5". Now look at your hand........ is that really that big???? Just get the best sub you can afford. Something like the hsu vtf3 should be small enough. If you don't want to move furniture 2-3" left and right just keep what you have or ask yourself why you have so much stuff in a room that you can't accommodate another few inches.
Or just get some real supertowers that'll have even more bass then a svs pb12plus!