upgrade path from my current speakers? (Dynaudio Special Forty)

Funny you mentioned the sound of the special 40. I went through the exact same scenario. Found a good deal on a pair of Heritage speakers. I had  them awhile but they just did not engage me like my 40’s I sold th Heritage and bought an another pair of 40’s. I keep several speaker and amps as I like to change up sometimes. My PassLabs and my 40’s are my best combo.

Given that you like the dynaudio sound, I would think the confidence series would be the most natural path. I've had a chance to hear them a few times and they sound really good, the only negative I heard is i thought they lost a lot off axis 
 

I have a pair of the HS’s after auditioning the SP40’s in my home. My Pass Lab INT 25 sounded great w the 40’s but not as good as the HS’s. I brought in a PL X250.8 amp and now the HS’s jumped to a new level with more of the Dynaudio sound. I noticed the cymbals and highs grabbed my attention and became real. The upper bass was fast tight w incredible dynamics. What turned these amazing speakers in to was adding a sub that could keep up the HS’s so I added a REL S510 and spent time dialing it in. It filled the lower register and it doesn’t miss a beat w the HS’s. I’d like to try adding a second sub as I’ve heard it’s even more incredible.
this setup competes w $20k floor standers.   

I have to agree with @ghdprentice. You are focused on the speakers, but there’s a lot more out there than Bluesound , RME and NAD. Bring your RME into a dealer and ask them to demo it against some other dacs and see what you think. 

Subwoofers can help a lot. Also, nothing about room conditions have been mentioned. These are the two factors which allowed me to get amazing bass with standmount speakers (Fritz) and also with towers (Ascend). I'm not spending nearly the money you are -- no shade, there at all -- but without the room/sub factor considered, I believe the lower frequencies can be an endless chase.