@keeferdog
My room is a little larger than yours - 14 x 26 x 8 1/2 basement room, poured concrete floor and wall behind the speakers. Other long wall faces outside (walk-out basement), other two are interior framed finished drywall. BIG speakers with BIG subs. My problems were much less severe than yours. That said, here are a few suggestions.
I suggest that you go to @home, Hobby Lobby or a similar type of store and buy artificial plants. Big and full with 2" to 5" long leaves, as tall as you can get to fit under your ceiling. If possible, put them behind your speakers, in the corners and behind you Small, maybe 4 foot plants, on the side walls between you and the speakers. They act as big diffusers. That will take care of sound above the upper bass. Also absorbs the sound to help "downstairs."
Bass might be a harder problem. Try decoupling the speakers from the floor. Try using books before investing anything. if you have some Vibrapods laying around try those in the correct rating. Spikes might not help because they are coupling the speaker to the floor.
I'm using the plants in this manner and it works great. Just a suggestion for the floors without any experience to back it up.
