Don't block drivers. Especially, don't block drivers producing one frequency range while leaving others uncovered.
If you have a choice about the furniture, go with cloth covering, overstuffed sofas. They will absorb some sound, which will be very helpful in that room. Use the thickest carpet or rugs you can and if you can't manage to get acoustic traps for the walls, hang tapestries on the walls. Make everything in there as soft and absorbant as you can, or that room will ring like a bell. And move your main speakers out into the room as far as you can stand it.
Given what I think the room dimensions are, this room - I don't say this often - is a prime candicate for some sort of electronic EQ. If you get enough absorption around the room to cut down the ringing, you'll have enough that the treble is a little attenuated and you'll want to boost it some.