Upgrade in which areas?
If the answer is just general sound quality, meaning that there is no concrete flaw that you're looking to fix, then no matter how much you'd spend, it'd all be for naught.
You do not magically get better "stage", "depth", "definition", "slam", "authority" etc by spending more. Doesn't work like that.
The only components that can affect those attributes are headphones, the digital masters, and DSP.
DACs and Amps OTOH, either work and have sufficient power, or they don't. There is no sliding scale, once you exclude cognitive bias from the equation.