No way you should upgrade your subs for $1,300 since you are 100% HT. After all, exactly what does an explosion sound like? Or all the other sound effects that are man-made?
If you were 50/50 HT and Music, then it might make sense to spend $1,300 to upgrade and even then you would probably be better off with a couple subs from Rythmik since they make arguably the cleanest subs short of the Submersive.
Save your money for a really big upgrade, which might not even be speakers of any kind. Look at your entire system and decide where you can gain the most impact. For example, if you are not using a front projector, you might start saving for a 70 or 80 inch Sharp LCD TV. I saw the entry level 70 inch Sharp LCD TV for $1,950 not long ago. A 70 inch TV could provide a huge amount of impact in your TV viewing.