Weak Link in chain as I upgrade from mid-fi?

Those speakers are very nice, but BOOKSHELF, inefficient and frequency limited.

The most improvement you can make is to replace them with full range. I prefer no vents, if vented front facing like your existing ones are.

Efficient, so you can drive them with lower wattage, lets you use smaller amp which saves money, less heat, more placement options, especially if remote sensor involved.

IF you try subs, agree with soix, TWO, a stereo pair, front facing, adjacent to your mains. Bass, fundamentals and their overtones are/become directional, a wonderful part of imaging.

Just saw this review of the new Gustard R26 DAC and think it should be very high on your list of potential upgrade options.  I trust this reviewer’s ears as his take on my Musician Pegasus DAC very closely mirrors my own impressions, so when he says the R26 performs very near the level of the incredible and much pricier Denafrips Terminator Plus this comes across to me as a no-brainer level recommendation.  Heck, buy it on Amazon and return it if it doesn’t just blow you away, but that seems highly unlikely.  While I’m very happy with my Musician Pegasus, if I was doing it over that is absolutely what I’d do.  But, I still think as good as the R26 may be and as per my prior post, adding a couple good subs will make the most significant improvement to your system and your enjoyment of it on an absolute basis.  Once again, FWIW. 

https://soundnews.net/sources/dacs/a-new-point-of-reference-gustard-r26-discrete-r-2r-ladder-dac-review/

For a small to medium room the Sonetto 1 is fine. I would have popped for the Sonetto II but that is me. I prefer a hi quality 2 way like the Sonner or QLN over floor standers. I have small REL T Zero’s to fill out the lower registers and have tuned them to my treated, small listening space.

Just my thoughts.
first of all, you have done a good job building what you have. Second, I am so glad to see you did not mention cabling as I don’t think they really make a bit of difference at this level.
I would recommend a stand alone DAC. I would not get a DAC/streamer combo. Too much is changing in the streamer market to lock into a single dual use function. The Bluesound node will work fine with an outboard DAC. I suggest you look very closely at the offerings from Gustard. The x26 Pro ($1,500) for a delta-sigma DAC or the R26 ($1,650) if you want an R-2R/Multibit DAC. Both offer fantastic sound at a great price point. Lastly I would upgrade speakers. I always buy speakers for my NEXT amplifier as having them as the strongest link is always the best path IMO. If you like the Sonus Faber sound, have a look at the Dynaudio line of speakers. I feel they offer more value in speakers with out flashy leather wrapped cabinets, etc. personally I prefer stand mounts. I own Dynaudio Confidence C1 Platinums (now discontinued). I would suggest trying the Dynaudio Contour 20 or 20i, Heritage Soecial, or the Confidence 20. All are amazing 2-ways and can run alone or be complimented by a sub for only the lowest octaves as they go down to ~35Hz.

enjoy the journey.

Stick to your gun.  SF Sonetto 1 is an excellent pair of speakers.  Ignore some forumers' dissing here.  I am not sure about the SQ of the internal DAC of SA20 or Node 2i.  I have heard audiophile comments about the so-so sound quality of the internal DACs in Node 2i,and a variety of the integrated amps.  To fulfill your curiosity and if you want to invest on a DAC, the highly raved Schiit Bifrost 2 is a good start under $1k.  Sky is the only limit if you go beyond that price range, which diminishing return will start kicking in imho.