what is the best way to deal w/ an asymnetrical ..

TacT RCS 2.0 or 2.2. Best room correction I've heard, and one seems to be up for grabs here (no affiliation).

Seems like you'd want to have some absorption sound panels, or perhaps simply enough absorptive objects, along the solid wall opposite the opening to balance out the two sides. The imbalance would be that you are getting no reflections from the open side, while getting a direct reflection from the wall opposite. Rives would be a good resource to answer this question.

Marco

I have a similar problem in my listening room. What I would suggest you do first is: THE PLACEMENT!!!
CARA software is very good, if you really want to approach it in scientific way.
Then, I would second Maggieq advice on TacT RCS 2.0 (or if you also want an updated DAC AND ADC 2.0s, OR 2.2X).
I just bought TacT myself, and let me tell you: the difference is not insignificant. I don't know if you can possibly reproduce it, using anything else, other than a room correction device.
And, of course, room acoustic treatments. Good luck.