Small dedicated listening rooms

" Potentially downsizing from a 17’ x 22’ room to a 8’6 x 10’ room. "
A nice pair of Sennheiser HD800S is what you need.

Closet indeed. Don't waste your time and $$$ trying to shoehorn a high end system in there. Do what has been proposed and invest in a very nice headphone rig. 15k wil go a long way in this situation.

Oz

I would consider Omega speakers and a quality set amp, perhaps even  LTA microzotl, in a very near field setup. Save you lots of dough too.

Duke brings up some very good points. Adding multiple small subs is beneficial, as it will smooth out the overall response. Unfortunately, adding more subs brings its own problems...and that is getting them to blend invisibly into the mix. Not to say it cannot be done, as I have managed this in my room, but it is more difficult to achieve and will take a lot more effort...and patience.
I wouldn't go with the headphone suggestions...no need to.
Since the room measures well and has a high ceiling, I think you are fine.

One of the best high end sounds I ever heard were big MBL 101D speakers situate in a room that was hilariously small, truly "closet-like" and I think smaller than the OPs.   But they were essentially nearfield, and the room well treated.

I've heard other speakers in very small rooms work well.  It depends on the speaker (for instance, something like Quad ESLs won't have as much interaction to the side walls), how you can position the speakers, what type of room treatment you can apply if necessary.

My first thought for the OP's situation was similar to what other's have mentioned.   Closer to near-field listening, and choosing an appropriate speaker for that.  But he mentioned the speaker has to be placed near the back wall, so, really that's the type of criteria that makes answering the question a lot tougher.