My room is 14'x12'x9' and I'm using a pair of monitors right now. I also have a pair of floorstanders that I use too (just interchange them from time to time). In both cases, I bettered the sound of my room by using a set of DIY Room Lenses. They give more detail, air and a wider soundstage. For $60-100 a set/3 you can't do wrong. I also use a carpet over my hard floors(ceramic tyle over a cement foundation), courtains to cover my glass windows, two DIY accoustic panels at the front corners of the room, and a DIY 72"x30"x2" decorative foam panel behind my listening position that helps to absorv the back-reflecting sound.
Even with my monitors (Madisound Geminies with Dynalab drivers in D'Appolito) the bass is pleasent enough and don't need a subwoofer.
Before investing that sum of money for the new speakers, try:
1- to move things around using different settings,
2- move your speakers around at different lenghts from back/side walls,
3- a near field configuration do the trick sometimes, even when you get used to seat farther,
4- have someone near you with Room Lenses to take them to your home for a demostration (or check how to make a set at www.audioasylum.com tweaker asylum).
Keep us informed and good luck.