My installer managed to fit a pair of 6.5's back there... dont ask me how, i was suprised, and they sound great. At first he was like "you dont want too much back there, the soundstage should be up front" but i have matching 6.5's in front and back, and when he heard them e agreed, the rear fill was perfect. Also have a 12inch sub in the spare tire well in a custom enclosure. Sounds great.