Difference between Bluesound Node, Node 2, Node 2i, NodeX

One big difference is that at some point (not exactly sure which model) there was a USB output implemented.

The original Node was the big, ugly, plastic cube. The Node 2 was the introduction of the current form factor, with a new DAC. The 2i introduced AirPlay2 and dual-band wi-fi. I believe it used the same DAC as the Node 2. The next gen Node (N130) had an improved DAC, new controls on the top, and allowed USB output. I believe the N130 also changed the plastic material of the case. There were complaints that earlier Nodes had their soft plastic cover deteriorate. The Node X again improved the DAC, as well as the headphone output.

I'm sure the different DACs all sound different. How much better each generation sounds will depend on the quality of your system. I find the difference in DACs among my Node 2i, Denafrips Ares II, and Meridian Director to be subtle.

Knowing now how much difference a DAC can make, I would not think that beyond the DAC I would be able to hear any difference between the Node models. I might convince myself I could hear differences, but I'd be lying to myself.