In terms of your budget, I would second the suggestions for looking at Schiitt DACs. I have a Gungnir multibit that I like quite a bit. I also have a Mytek Liberty II and I've enjoyed that but the top end has to be tamed a little bit, so depends on system synergy. I also personally don't love the user interface on the Liberty, but I do like its being fully featured with a top of the line chip.
If they make any difference at all, IMHO digital cables and similar tweaks would be quite secondary in terms of priority - get a well constructed DAC first and then see if you need to worry about that stuff with a later separate budget.
And I agree that speakers can make the biggest change in a system, and even adjusting their toe-in can have a huge impact.