How would you spend my next $5K?

#7, expanding horizons.

As a long time LP guy, this is not a good time to start going deep into vinyl record playback. Records, even the crap I considered standard "used bin" that was 4-8 US dollars, is now 30 dollars plus online and optimistically graded. I buy mostly old records, and mostly obscure stuff. The new "audiophile" stuff is also pricey for what it is and there is a lot of bad vinyl out there. 

I agree that adding a second sub might improve your overall presentation. It is very hard for me to make recommendations without hearing the system in situ, how it is set up in the room and what is "missing." I would assume that your system does not commit errors of commission but omission. That's an assumption, though.

I guess the real question is-- where are you dissatisfied? 

I find audio reproduction systems require gradual improvements over time-- once you finesse the set up and know how the system interacts with the room, you can concentrate on improvements. I also don't buy into "miracle tweaks." I think you build upon the strengths of the system by looking to improve the weakest link. What is that, in your estimation, OP?

Helpful comments, thanks.  I could say that  the Kensingtons and S/812 don’t fully pressurize my 15’x21’ space, though I’ve made some recent improvement in dialing  in the sub.  
 

Interestingly, my small bedroom (10’x12’) NAIM UNITI ATOM/Tannnoy MINI AUTOGRAPH/REL T5X fills the room very nicely with a good visceral feel.  Perhaps small room size and near-field listening helps this.  

+1 on a second sub.   Its benefits are beyond pressuring the room, but that is an obvious benefit.  Two generally support the image and soundstage and disappear more easily.

I would buy myself new speakers from your 5K and also buy you a beer and tell you how much I enjoy my new speakers from your 5K :)