Keep what you have and get a small sub, or get two (even better). Your room is too small to worry about getting the system to be loud enough. You will, for the most part, be listening "near field", so the LS50s will be perfect; plenty of sound pressure for your room size and wall reflections will be less of an issue. Depending on what low frequencies produce excessive resonance in your room, you may want to consider DSP.
If you just "like" big speakers, and don't like subwoofers, you will never be happy until you pack a pair of Klipsch horns into the corners.