If you want really good 2-channel performance you'll have to get the Denon outta there as both the preamp and amp sections will both significantly limit your system's potential. But the good news is you can keep the Denon to do surround processing and power the center and/or rear channels.
I'd focus on a good stereo amp first, because it'll be important that it's a good match for the Josephs. Something in the 100 watt range from someone like McCormack, Marsh, or Odyssey would be cost effective and trounce the amp section in your Denon. Next, find a good stereo preamp -- again, Marsh, Odyssey, and McCormack all make good preamps, but the McCormack offers a HT passthrough that will let you seamlessly integrate it with your Denon(i.e. no volume matching necessary). Not a must have, but a nice convenience especially if you have others using the system.
Hook your stereo source into the stereo preamp and the stereo preamp to the stereo amp, and you've got a pure high-end system for stereo listening. Hook the front L/R preamp outs from the Denon into an AUX or VIDEO input on the stereo preamp, and voila, you've got an integrated high-end 2-channel system integrated into a HT setup. When you want to listen to high-quality stereo music just choose the proper source(i.e. CD), and when you want movies or surround music just choose the AUX or VIDEO input on the stereo preamp and the Denon once again controls the whole setup. Pretty neat.
You will notice significant improvements by adding a better stereo amp or preamp, but adding both will almost certainly give you that "leap out of your seat" experience you're looking for, and it will allow your Josephs to really open up and show their full potential.
If you're intent on listening to music in surround modes you might consider a 3-channel amp and a new surround processor, but now you're talking a much higher outlay of cash. If you build a really good 2-channel setup as outlined above your desire to listen to surround music will be greatly diminished if not obliterated -- better to leave the surround stuff for the movies, at least for now. Hope this helps and best of luck.