You have a large size space and you're trying to fill it with a small stand mounted monitor. The tonal balance of the reflected sound, which is the majority of the sound in a large room, unless you sit very close to the speakers, is thinned out by the size of the room. In effect your room is working against your speakers. Obviously you need speakers that will work with this room. The problems is I'm not sure you can do it within your budget. The bigger Ohm Walsh speakers might fit your needs, but they are well north of $1,500. Vintage corner horns would also work, but again decent ones start around $2,000.
My suggestion is to not make any changes and live with what you have. Save up and come back to the question in a year or two. You'll have a better idea of what you need and a larger budget.
My suggestion is to not make any changes and live with what you have. Save up and come back to the question in a year or two. You'll have a better idea of what you need and a larger budget.