Moving up from a Node 2i

Stock rPi USB out measures extremely well and I love mine. That said, I recently bought a used Krell Connect that is amazing, but I'm using the krell DAC out, fully balanced differential etc. Probably a bit out of your range even used. 

I've read good things about Lumin, Audiolab, and Technics streamers, and have them all on my "to try" list. Good luck!

You should be able to snag an Auralic Aries Bridge for a grand.  While the software isn't nearly as good as ROON, Auralic does make both the h/w and the controlling s/w - so it will 'play nice' together. One drawback, however is the fact that the software does require an Apple iPAD for the controller (any version should work) and you can pick up an older one for $100 or so on eBay or Amazon. You can use with a dedicated USB flash drive, USB SSD or a NAS (network attached storage) drive. Not the last word in fidelity, but overall I've been very pleased with my investment.

All, I always wonder about this too - can someone explain how the “delivery mechanism” (my phrase) of the 1s and 0s of a digital signal can make any difference, and to the extent it does, why is that? I also have the node 2i and am tempted to sell it, get a better dac and run a usb from my iPhone and play tidal.  My understanding is that iPhone will unfold mqa. How would this be different than using the node as a streaming source if it just delivers 1 and 0s? I appreciate everyone’s anecdotes but can someone explain the technicalities? 
That said, on another system using a Schiit dac, data from a cd transport seemed to outperform my Tidal phone stream of the same content via USB. I can think of no technical reason for why this should be... but it does leave me with the uncomfortable idea that a “better” streamer - e.g. the AlloOne products - may have merit to the extent they eliminate electrical noise from data delivery. 
Please share your thoughts. 

My thoughts is it has more to do with the hardware and software of the delivery  mechanism. I like my Node2i  to me it sounds good in my system but I know something like a Matrix Element X uses much better hardware from the dac to the controllers for USB and digital inputs. 

Noise ingress and egress and jitter are issues with transports/streamers...

Amir does an excellent job of covering jitter...
https://www.audiosciencereview.com/forum/index.php?threads/digital-audio-jitter-fundamentals.1922/#p