This is sort of "out of the box" but have you thought about some room treatments?

I don't think upgrading your receiver or components is going to change yuor sound that much (opinions vary on this topic). Maybe your room has some imperfections that could be fixed with some new drapes, carpet, sound absorbing panels, etc.

At the very least, maybe you coudl use the money to invest in a set up disc and an SPL meter (if you don't already have one). This will really help with the soudstage and depth issues.

Let us know what you decide.