AMP or Preamp

Definitely upgrade amplifier before anything else. You need a high current amplifier cos the Sasha’s impedance dips very low around 80 Hz.  I stand corrected on 80 Hz. 

Lots of good suggestions.  Going to take some time digging into all this.

Upgrade the preamp first. Get the one that is better than the built-in preamp section of your Yamaha receiver. I think your Hegel DAC is probably good not sure I haven’t heard it before. Hegel generally makes good products. If you plan on keep using the Hegel DAC with a Bluesound Note streamer I suggest you look for a pure analog linestage preamp (no DAC). The McIntosh MC2600 preamp has built-in DAC.

Your Rotel RB-1590 power amp is pretty good, and especially for its MSRP of $3k it is really good. I’ve heard this amp before driving the B&W 803 D3 speakers and was very satisfying. Also got plenty of power reserve on tap to drive just about power hungry speakers out there. It drove those B&W 803 D3 with ease and effortlessly. Of course there’s always room for improvements especially to pair with your Wilson Sasha speakers. But for now I would focus on upgrading your preamp and upstream electronics first before the power amp. 

I'd go with the Mcintosh C2600, outstanding across the board.  Then match an amp to the C2600.

Look for a used ARC linestage preamp preferably their Reference series preamps such as the ARC Ref 6 or Ref 10 if you can afford them cause these ARC Ref 6 & Ref 10 preamps (especially the Ref 10 pre) cost many times more than the Mac C2600 preamp. Then get the ARC Reference series amps or you can still keep using your Rotel RB-1590 power amp for now and then upgrade to the ARC Reference series amps later down the road. ARC (Audio Research) gears pair really well with Wilson Audio speakers. McIntosh gears don’t sound good on Wilson Sasha speakers. McIntosh gears sounded good on Sonus Faber speakers though. Those are pretty good pairings.

The ARC Ref 6 or Ref 10 preamps will be a huge step up sonically from the McIntosh C2600 preamp. All ARC linestage preamps are pure analog linestage preamps (no DAC).