I have listened to both. They are both fantastic pieces. They do sound different. Two things I heard that were genuinely different were the way each amp handled bass and the way each amp handled human voices. They were different, and I believe many people would differ in their asessment of which one they preferred.
I genuinely believe that, depending on your speakers and room characteristics, one of these integrateds could sound better than the other. I also believe one could genuinely prefer the general sound of one over the other (in either direction). For me, I preferred the 6900, I also needed one blanced input, so I went with the 6900.
I don't think a person could go wrong with either, its choosing the one that best suits your needs and taste that is the key. You must, must, must, must, let your ears be the judge. Enjoy!
