I agree with @stereo5 that the biggest improvement will be in your speakers which may be the weak spot. However, I also agree with @ghdprentice in the importance of the preamp. And this too is a weak spot. Which is the biggest bottleneck is hard to say.
You may be surprised at how much more Rel subs can add to the speakers. They magnify not just the bass but the whole freq range This makes for much better imaging. So that may be your best option. But at some point you need to upgrade your preamp. Tubes should be considered
You may be surprised at how much more Rel subs can add to the speakers. They magnify not just the bass but the whole freq range This makes for much better imaging. So that may be your best option. But at some point you need to upgrade your preamp. Tubes should be considered