So now I'm back to bridged mode and I like that much more.
I've tried passive bi-amping several times, and always ended up preferring a single more powerful amplifier channel as well. One time I had a 5 channel amplifier (125W x 5), and 2 of channels were just sitting there unused so I bi-amped the main speakers, and it that case it was a little
bit better than not using them at all.
But going to a more powerful 200W + amplifier was better yet than the lower power bi-amp setup. The more powerful amplifier had more reserves and dynamic power to give the speaker what it needed when it needed it.
So that's my personal experience with passive bi-amping. If you have extra channels of amplification lying around (and the amplifier cannot be bridged) what the heck, go for it. But if you can bridge the amps or are able to replace them with a more powerful amplifier, 4 times out of 5 you'll probably be happier with the results.
BTW, many bridgeable amplifiers when bridged can't deal with lower impedance 4 ohm (or less) speakers as the bridged amp often sees half the impedance (2 ohms or less). Apparently the NuPrime amplifiers don't have this limitation.
Active bi-amping with an active line level crossover (bypassing the speaker's internal passive crossover) does have a lot more potential, but that also comes with additional expense and complexity.