I need an audiophile quality DSP with balanced connections (XLR / AES) to tame the bass bloat in my Harbeths when driven by tube amps.  I’ll spare you the details... but... just need a quality 
DSP with balanced connections.

I guess I have a Behringer 24/96 Equalizer - I could try - its used with my Emerald Physics OB speakers.  Not sure it has the automated dsp, but it would allow me manual control.

The Minidsp DDRC-22D does everything in the digital domain since you say you don't want a DAC. 
That’s the one I’ve kinda focused on.

There is no problem with my Hegel H590 or Class D Audio SDS 470C amps, just my ARC Ref 150se. So... it's not the room... its the amp.
You might know that I'm a tube amp manufacturer (that also holds a patent in class D amps as well). Take it from me on this bit (since the solid state amp is fine, we'll assume that a DBA isn't needed): speaker cables can affect tube amps a lot more than they affect solid state! So I have two recommendations: try several different cables and keep the cables as short as you can: under 3 feet if possible, and make sure the connections are tight. I would also try different taps on the output transformers of the amp as that affects things too- sometimes counter to what you might expect.