any suggestions on what to replace Bluesound Node 2i with

$4200 for a streamer! To heck with that. $4200 would by a hot turntable/tonearm combo. You’ve got your priorities mixed up. Turn to vinyl for real music. IMHO. 

This biggest improvement in my opinion is getting a QUALITY DAC the DAC in the Node and Node 2i are fine for well lo-fi listening.

The new Node (no longer called 2i) has a better DAC that the 2i but it is still lacking.

I use a Mytek brooklyn bridge(version 1) and love it. It is a roon endpoint and sound is great.  I believe they just released the second edition which is still under your budget($3500) or you could find a version 1 used possibly for less.  Nice thing here is, it is a streamer and a great dac so you can run the bluesound through the dac and do some a/b comparing with the internal streamer of the mytek and use the winner?  I have compared to streaming through usb (through the Mytek)and the mytek streamer via roon always wins(ethernet)
I bought an astron rm-12 power supply for mine and it really helped the sound.
Highly recommended.

@Coltrane1  I see your point but I'm not getting a turntable. Never

@coltrane1 Not sure if you stream but there is nothing like having unlimited access to music at my fingertips with my iPad as the controller. Just can't beat being able to choose not just any album but play any song in any order