Dill 1
Bring your listening position to 10' from the speakers. Put your speakers 10' apart (measured at the center of the tweeter). Position yourself 10' from an imaginary plane between the tweeters, dead center. Angle both speakers so you can see just a sliver of the inside wall of each speaker at your listening position. Also, adjust your listening position so your ear (height from the the floor) is as close as the tweeter height is from the floor. Do not use a cloth covered , high back chair for listening. I would also suggest shorter, higher quality speaker cables, but only after you have done all of the above.
I wondered about being 17 or 20 feet from the speakers and would start with the basic stuff like dill1 suggests; and then incremental adjustments to try to improve the sound.
Also maybe the odd room shape is disrupting the treble, and some sort of room treatments are necessary.
If it is the room, spending for new speakers may be a way to waste your money
Or maybe you just want new speakers?
FWIW
Dsper.