need help choosing between paradigm ultracube 10

and ultracube 12 sub,
I have the 10" to try out, I feel its lacking depth, my family room is 20x17, I have an open floor plan. I'm using a marantz sr5004 90w receiver(not sure if I should upgrade to 6004 110w)love the receiver but questionning power for sub? using B&W 602's speakers. I turned up the crossover to its max I have the receiver set at 100 hz and phase control turn up to 2 oclock (sound better that way) level is at 12 o'clock. I'm not as knowledgeble as most of you guys but would love any input you can give me, would the ultracube 12 make a noticeable difference? upgrade the receiver to 6004? or just get a bigger sub.
Thank you