What is your living situation? Any spousal acceptance factor to consider? 20x30 is a big room, how far apart are your speakers? Flat or vaulted ceiling?
Some things I have done in the past was to go to Home Depot and get some 8x10 area rugs to get onto the floor, and have picked up some small woven decorative rugs to hang on the wall, or you could make your own frames and build your own room treatments by going to the fabric store. Anything that disrupts or absorbs some of that flat drywall will help. Drapes, house plants, etc.. Spartan is the enemy of the good when it comes to acoustics I have found.