I don't know what cables you're using and how much you're willing to pay, but I'd start with a new processor. The Arcam AVR100 stomps the Denon, IMO. You could get one for around $500 used. If you want Pro Logic II, get the AVR200 for around $750. You'll definitely hear things with the Arcam that you're missing with the Denon. The Denon always sounded a little light and tinny to my ears.
Next, get a pair of Kimber Heros for under $100 for your mains. They would expand your soundstage, and give you a more dynamic, open sound.
Good luck.
Next, get a pair of Kimber Heros for under $100 for your mains. They would expand your soundstage, and give you a more dynamic, open sound.
Good luck.