DAC? how much more $$$ to get a significant improvement over Bluesound Node?

Bifrost 2 is what I use and think that it sounds killer. I also put a good power cable on both and have seen an additional improvement. Good luck!

Denafrips Pontus ll dac would be a good choice.

yes depends greatly on the quality of the rest of your system

the current node's onboard dac is said to be improved somewhat over the one in the prior '2i' version

still, there is a lot of upside if the system in use is good and resolving

It doesn't take much to better Bluesound by a wide margin, for your budget of ~$3K, used Denafrips Terminator 1, or Holo May Spring 3 would be about the best value for money.

Avoid dacs focus only measurements but sound like cardboard cutouts, like the Benchmark and Topping.

Probably any outboard dac that’s a known company would best the node. 100 bucks and up, pick your poison