Best bang for the buck subwoofer?

[dazkyl]

So, at the moment , i got my 5.1 set , with my 8'' subwoofer placed in the front left corner , on the opened side of the room.After some bass testing on movies , i noticed that an 8'' sub is not enough for this room (4.3m x 4.6m) , and when i try to dial the knob volume up past 9 oclock , it starts to rumble.I mean when setting it to 9o'clock the bass is pretty smooth but not what was i expecting.Im expecting a much tighter and i mean tighter bass . I think you know what i mean. So i was planning to find a sweet spot for my current small subwoofer near the couch / listening position , and add a 12'' subwoofer in the front of the room in a corner where my current 8'' is.

At the moment , with my current 8'' sub , i set my fronts to large because im getting a much tighter bass with fronts set to large instead of small.

I had in mind to add the Jamo sub 660 (12'') along with my current subwoofer jamo sub 250 (8'').

This is a picture of my setup in the room. I had in mind placing my current sub (its behind the christmas tree) back near the piano and the snowman , and the 12'' sub behind the christmas tree.

Feel free to suggest ! Thanks.