Active bi-amping is the ultimate goal that I was striving for, but unfortunately it's not possible with my ReQuests due to the fact that I cannot get rid of the internal crossover. In this case, the next best thing is to bi-amp passively with high-quality tubes on the panels and solid-state on the woofers. The rationale being that I'd like to have a minimalist tube amplifiers to try and preserve the purity of the signals on the panels. This means that I'm looking for an medium powered amplifier to keep the number of components in the signal chain down to the minimum. The SixPacs with 60 triode watts fit the bills nicely. I'm lucky that the ReQuests has only 1 crossover point at 200hz and this is below the all important midrange frequency that human ears are critical of. So, in this particular case where the absolute (theroretical) quality of the crossover may be compromised a bit, I can afford to bi-amp my ReQuests passively. To further clarify, I would not passively bi-amp if the frequency in question hovers around the midrange area. Sure, my SixPacs could benefit somewhat if there's an active crossover preceding them, but then I knew to look for a beefy amplifier with robust power-supply to serve in a passive bi-amping configuration.
The answer to your question is a resounding YES, I do notice a huge different going from a big powerful amplifier (bi-wiring) to passive bi-amping with tubes on the panels. This way, I get the beautiful tube midrange on the panels and powerful bass from the solid-state amplifier. I feel that going with a bigger amplifier, I would lose the finesse on the mids and highs just for the sake of being able to drive my ReQuests full-range. I guess I was lucky that I was able to put together all the pieces to fit my puzzle after considering all the factors.
Spike