Acoustic treatments. Make use of GiK Acoustics' and Auralex' room analysis services. Possibly even hire an acoustician or acoustics engineer from a company like PMI or Rives Audio to take measurements of your room, since it sounds like a complex acoustical environment.
Two things really make a difference: the room's acoustics, and the speakers. Changing either can be transformative. And acoustic treatments can look very attractive these days. Suede panels, patterned panels, or panels with actual artwork or images printed or dyed on them are all available. Naturally, the more elaborate the look, the higher the price. But the point is that acoustic panels need not be big, plain and ugly.
So, get some acoustic advice that's specific to your room. Start with the free services and go from there as necessary. Then treat your room with products that meet your requirements and desires in terms of looks.