Warren: The 7 is a "funny" amp. Take a look at the power ratings if you doubt this.
Other than that, i've commented on the inability of Bryston's to deal with low impedance loads in the past. When comparing the 7 to other amps of lesser power, Stereophile went out of their way to let us know that the 7 was not capable of driving low impedance loads with any type of authority. Not only did the sound deteriorate, but the amps went into clipping sooner than the others. This is true even with amps that were rated for measurably less power. For sake of clarity, i had posted such thoughts on Audio Asylum long before the review of the 7 was printed. That article only helped to confirm my suspicions and experience.
El: By using a powered sub, the bottom end is filled out and the sound becomes much more authorative at lower volumes. As such, one can typically reduce spl levels slightly by achieving greater extension and fuller output with less drive applied to the mains. If you've got tone controls, turning your bass way down and listening to the music will alter your perception of spl to a great degree. This is true even though the upper bass / lower midrange on up go relatively unaffected.
I think that the point that Cytocyle was trying to make was that if the mains are actively crossed over to reduce bass demands, power levels are also reduced. This lowers the potential for clipping i.e. excess midrange and tweeter energy. While it might be hard to believe that such a big amp is clipping, you might be surprised at how different designs respond under duress to various reactive loads. Sean