The short answer from me is no, I haven't heard the ESL 9 biamped, but have heard it. But, I had the Vista for about 7 years and found that I needed to biamp and was very happy with the result. The ESL 9 is what I would call a nice improvement of the Vista which also had a 9" panel but only one woofer. So the ESL 9 is better for bass response, and is crossed over at 380Hz (better IMO) vs the Vista's 450Hz.
I biamped with a 5 channel amp and always wanted to get separates, or at least two stereo amps, but just never got around to it. FWIW, at lower volume I never felt the need to biamp. It was only when I was pushing the volume to fill the room that I would notice an improvement when biamped.