any suggestions on what to replace Bluesound Node 2i with

The ifi device is very interesting. 

Yes I would look at the Cambridge streamer before dropping $4500 on one. 

Have you tried a different connection than optical with the Bluesound?   That alone might make a difference. 

When it’s digital it is not hard to make something sound different as desired . So no doubt streamers can sound different for many reasons. Outboard DSP is likely to be able to reproduce similar results.
I think it’s better to say I have never heard bad sound come from a streamer through a good DAC, not that they all sound exactly the same.   

Personally I have not heard significant differences between streamers to same DAC with CD res sources. . Never heard a bad one. Interface type used can matter. Asynchronous USB is the way to go with most modern DACs. I only use wireless internet connections to isolate the streamer from any noise that might exist on a wired connection and find that works great though some claim a good wired internet connection is better at least in some cases perhaps with hi res sources where wireless bandwidth perhaps could come into play.

If the issue is sound quality and not other user functionality then suggest trying an external USB  dac with the Bluesoimd streamer for comparison before dropping $4500 on a new streamer/dac.