You are fortunate you can listen to both before purchasing. The 6900 has autoformers, which is a good thing. During the audition have your dealer try the B&W's on both the 4 ohm and 8 ohm tap, see if you hear a difference. Then go to the 6500. You will probably like one set up a little more, if not, base your decision on these 2 things: The 6500 is cheaper or, the 6900 is more future proof with more power and the autoformers. One of those will make more sense to you. Good Luck
