Just thought I would toss my 2 cents in, having actively biamped my Vandersteen 2ci's with Bryston gear.
I ran them biwired with a B-60 Bryston for about a year before I 'went for it' and got a 2B-lp. On the Vandies, it was difference that although subtle at first, really made a big difference.
Similar to when I upgraded the power cord for the B-60, but 'more'.
I lived with the system like this before getting a good deal on an X\O and going the little bit further. Once again, at first subtle, but big difference.
Best way I could put it was that details fleshed out better, bit by bit.
DID it make a difference in my experience? Let it be put this way: I needed to sell the 2B-lp to pay for my wedding and ended up unable to listen to single amped setup and turned it off for months. If I couldn't listen to it as well as it could play, I couldn't bear to listen to it.
(I think I was clinically depressed!)
I did end up getting another 2B.
In my 13' square room, I had all the power I needed, and although thought of bigger Bryston amp, never got around to it.
My personal experience has at least underlined to me that in my setup, even passive biamping was a great gain.
Good luck in your quest!