How do you have your speakers firing? Straight or with toe in? The more you toe them in, the more you will tame the high frequencies. As KR above mentions, room treatments would be first line of defence. You can try absorption/diffusion panels at first reflection points on the side walls and if your listening seat is right smack on your rear wall than a similar panel behind your listening seat (i would look for a panel with both absorption and diffusion or just diffusion in the panel behind your head). Finally, your choice of cabling can also tame a hot top end. Hope this helps.
