I just remembered that I did a 600 vs. Sony face-off last year. I don't believe I ever posted this but here it is. It was at that time that I discovered the 600 had a lower than normal input impedance.

Note the hump from 50Hz to 80Hz in the Sony and my comments regarding the lack of thump when I reduce the Sony's cross-over to 50Hz. The prices shown are what I paid. The bottom chart represents the maximum SPL I was able to achieve in my room. My room is 4,000 cubic feet and it is open to the rest of the house via an open stairway. The Sony believe it or not went louder but as you can see, I nearly killed it \:\) .