DSP TO TAME THE BASS IN HARBETH SPEAKERS

Plug the port.

When I had the Harbeth 40's and need to control the bass in my listening room I used a Vandersteen High-Pass filter between my ARC ref3 preamp and my Pass 250.5 or Quicksilver V4's. This solved the problem for all of my sources. You should call JohnnyR at the Audio Connection to talk about this. Good Luck!

running harbeths and tubes as well. i have tamed bass quantity and peak issues with the following-
1 modify speaker position- away from all walls, screens, cabinets and surfaces as much as possible, min 2 feet all directions.
2 stands- open frame stand with harder dots. soft dots between speaker and stands cause bloat. use clear silicone bumpers.
3 tubes- different small signal tubes will help drastically with bass bloat. new production and nos tubes seem to be bass heavy, e.g. eh, jj,, brimar. try some mazda or amperex, amperex off label.
4 cables, interconnects- different cables tend to be bass heavy. try van den hul, nordost, audience for less bass bloat.
all of the above can add together and should be optimized individually.  when you have done your best i doubt you will need DSP.  

to tame the bass bloat in my Harbeths when driven by tube amps

Sounds to me like its nothing to do with the speakers, or the room, and DSP certainly is not the answer. You're trying to make your tube amps have the same thin unsatisfying bass as solid state. I have a better solution: get used to it. If anything maybe try and figure out how to find SS amps that have as good bass as your tube amps. 

I know. But you can always try.

DEQX