Advice on dedicated room

@ chorus 

I have concrete on three sides with the two opposite concrete walls probably extending out an undetermined amount. I haven’t started anything yet so all options are open. I have a dedicated sub panel that serves the main floor home theatre that I will also use for the 2 channel room.  
@sensesundertime 
I consulted with one company that I believe was going to design Helmholtz in the room. I didn’t go with them because they said it would cost 50k when done. Far too much for me but I will still look into it. Thanks 

Agree 100% with millercarbon:

This small a room will also make it more important than ever that you use a distributed bass array and Townshend Podiums and Pods for isolation. The DBA will make your small room sound huge, and isolation will greatly diminish the rooms impact on the sound by energizing it less. Money spent on these will far outweigh a lot of much more expensive acoustic treatment.

I have had nothing but excellent results with a DBA in 4 different rooms (two of them smaller than yours).
Though I have yet to try isolation podiums or pods, I also got great results isolating with springs under each of my mains and also under each of my 4 subwoofers.

@artemus_5 +1:

Or set up the system in the corner facing diagonally into the room and leave the size as is.

I have a 15’ x 15’ exact square room set up very similar to figure 2 at: DECWARE - Article about Setting up a Listening Room without Treatments
If not for experimenting with this diagonal placement, I probably would have given up on the room.
Very noticeable improvement over anything I tried regarding "traditional" speaker placement.

Lots of great advice in this thread.
Great thread too! I’m sure a lot will benefit from the many great contributions.

OP - Best of luck to you on this journey!

We are all agreed you need to make the room more oblong.

Why not build a separate storeroom on one side for records, books, equipment, whatever.
Build about 5-6 feet wide reducing the 16.5ft dimension.
Clear all the crap out of your room.
I did this when I built my room.  I have art on the walls in place of loads of LP racks and a great open feel.

More than anything else it helps just to keep in mind. No room is perfect, and one can easily spend more on the room than the system.   

Back when I was searching around going to all the audio stores within a couple hundred miles the best sounding system by far was in a room just like yours. Corner Audio, only the long axis was vertical. The room was roughly 15x15 with a ceiling twice as high! Yet he had easily the best imaging, most engaging sound of any store up and down I5 from Seattle to Portland.   

That is the main point I would like to make. Harley has an excellent book, and there is a tremendous amount of information. These things are all about compromise. The more you know the more likely you will be happy with your particular set of compromises.