I hate how enthusiast forums of almost any type often end up blowing past the stated budget and recommending things way beyond that level. In this case though, I actually agree with the idea. $500 may get something different sounding, maybe a little better, but probably not significant improvement.
Moving closer to $1k should bring a much more obvious upgrade. Even if you have to wait and save for a while, that would be worth doing. I'd stick with second hand units to save big.
Right now for under $1k I can find listings for the original Auralic Vega, Metrum Amethyst, a few nice units from ExaSound, a Wyred4Sound DAC-2 DSD with Femtoclock upgrade, and a classic Sonic Frontiers SFD-1 mkII. All of those should make a large enough difference to be worthwhile and give you years of enjoyment.

