As Ronnie pointed out, it can be very room dependent. My 6Ks (D6000s upgraded to 18bit DSPs) didn't sound quitte as tight as the 7Ks in the HT in the basement; even with MRC they were a bit boomy. Once I moved them to a much larger room with a 14 foot celing and reinserted the 518 that had been lying idle in storage, they were magnificent - still are. The 8Ks turned out to be a lot more tameable within the more constrained space of the basement, and so relegated the 7Ks to rears. Point being, rightfully placed though they are in the above chart, my experience is that the 6K can sound worse than the 7K in the wrong room.

Main System: Trinnov Altitude 32-8-16, 271, 2 x 8KXE, 1 x 8KPP, 6 x M6 Surrounds, Rel No.25, Oppo 203, Zappiti Pro 4K HDR, Roon, WiiM Mini.