How to make small room sound bigger

A lot of absorption can make any size room sound lousy.  A sterile, dead sounding room will not sound bigger.

If you are serious about trying to get a room to sound larger, you will need to use additional channels of speakers and a processor that can send delayed signals to the speakers.   

What's with the list of speakers and amps ? Ones on hand or ones under consideration?  To make the room seem larger you don't want a lot of absorption. 

Combination of absorption and diffusion. Room acoustics vary from room to room. And some is personal preference. I would experiment with several different placement options. But yes, too much absorption will kill the room energy. 

Good luck and have fun! I've always found experimenting with room acoustics quite fun and interesting.

You cannot make the room sound bigger.  If you do a comprehensive acoustic treatment along the likes of what erik-squires suggests, you will get smoother frequency response, better dynamics and better soundstage/imaging.  A larger sound image in the same size room is the best you can achieve.  It will involve both absorption and diffusion along with a good deal of trail and error experimentation.

@ei001h 

I have that exact room size but with carpet over concrete. I did what @erik_squires  suggested, called GIK and worked with them to treat the room properly. I ended up with 12 of their 242 panels (4 on the front and back walls and a pair per side wall) which made a significant positive change to the sound of my system. Now, I can and may go further with GIKs suggestions but at the time it worked with my budget.

My system: Anthem STR Stack> Aurum Cantus V7F & Pair of SVS 3000 micro subs