Possible bookshelf upgrade


Hello to all.
Here is my question. In my bedroom I have as my mains a pair of Definitive Technology Studio 55. I am thinking of upgrading. I run these with a Marantz SR5010.One candidate is the Paradigm 15b. So, would I be gaining much doing this? They are in a 5.1 system. My budget is up to $2000. I have heard the Nola boxer, which is very nice. I am just not sure if at this range it would be significantly better. Thankx in advance for all advice.

arthurd
Well, if I am not mistaken, the DF 55s sell for ~$500. So with a $2000 budget you can most certainly get an improvement. 

Do you use this system for 2 channel music listening as well as for 5.1 movies? To me the value of the upgrade would depend on this.
Yes, it is part of a 5.1 system. I am also changing my primary listening  area as well. I have questions about that. . Not sure where to post that as I have questions about speakers and electronics.
Perhaps a pair of Zu Omen Bookshelf? I own them for my office and they are quite nice. Also, less than $2k.
Bob