The reason the 3A Sigs sound rolled off up top is because time alignment of the drivers allows all of the drivers output to arrive at the ear together (at the same time.) Most of us have been conditioned to accept the early arriving sound of most speakers tweeters as detail or transparency.
If you run a frequency test of the about 10KHz to about 18-20KHz, you will find that the speakers are not rolled off. Their off axis response is also good.
Time and phase speakers take a bit of getting use to. A simple sit down with them will not do. Once you have extended exposure to time and phase speakers, you will find it hard to go back to non time and phase aligned speakers. They just want sound right any more.
The other condition is they really do need to be precisely set up. This includes tiltback and ear height adjustments. If the demonstrating dealer does not measure your ear height vs distance vs tiltback, then he has not done you or Vandersteen justice.
Unfortunately, Vandersteens are a speaker you just cannot plop down and listen to without proper setup. It makes all the difference in the world.
The latest incarnations of Vandersteen's do sound a touch brighter and more open. Same basic sound, just improvements with time and technology.
His new 2CE Sig II's are about as good a high end bargain as you will find and follow the philosophy of the Quatro's (which are Stereophile class "A" speakers.) He has done many refinements to the 3A Sigs over the years also. A new pair doesn't really sound like the older ones. I would choose the new 2Ce model over an older pair of 3A Sigs.
As for AP, they're a little too hot for my taste and I found their soundstage depth to be somewhat limited to the sides. I never made a direct comparison. They stood alone in my listening room and this was just my opinion for what it's worth.