I sit in an office chair at the lowest setting and I'm 6'5" so my ears are 47" above the floor or a foot above the top of the speaker cabinets.OMG, that's most likely your problem. You are hearing nothing but high freq.
Just the way drivers are constructed, the acoustical center of a tweeter is more in front of the driver than the acoustical center of a woofer. Hence the sound from the tweeter comes 1st to your ears. That's also one reason you find time-aligned speakers (like Thiel, Meadowlark, Green Mtn Audio) slope their baffles such that the tweeter is physically behind the woofer plane. With your sitting a foot above the height of the speaker the drivers have no chance of integrating.
You need to move much lower so that your ears are about 1" BELOW the midrange woofer. This way the tweeter sound will have the longest path to your ears & the woofers the shortest. It will compensate for the tweeter's acoustical center.
besides a beanbag you might also try those canvas lawn chairs (the ones you take for 'music-in-the-park'). The canvas seat sags once you sit & drops you lower. I've used these canvas lawn chairs successfully.
Since you're so tall, your solution might be 2-fold: seat lower + raise speaker.
Let us know how you fare.....