Thielrules - it all depends. A very big deal is running out of power. The Adcom and Benchmark have overload LEDs. Listening at 95dB peaks at listening position, the Benchmark overloads consistently in stereo with one amp channel driving the woofer and the other the mid-tweeter. The bass amp can be bridged and its input sensitivity reduced to match the stereo upper amp. The upper stereo amp then becomes the overload limit, so it also must be used in bridged mono. Clipping is unacceptable. The Adcom at twice the power is better, but marginal on the mid-tweeter. It has no input sensitivity selector and therefore in stereo it cannot be easily gain-matched to the bridged woofer. So no go for tri-amping. Classe DR9 has similar power to AHB, so I assume it clips even though it doesn’t give LED proof. If you had 4 amps and could dedicate one to each woofer and one each to the two mid-tweeters, that is theoretically better than a single bridged amp to all three drivers, at twice the amp/cable expense. I am personally at peace with a Bridged Benchmark driving each channel with 3 separate cable runs or two runs: one to the woofer and another to the mid-tweeter.
To your question of best configuration - Because low impedance loads cause higher distortion in normal (non AHB) class A/B amps, I would prefer a stereo amp with one channel for the woofer and the other for the mid-tweeter. Those amps would need to be a few hundred watts minimum per channel into 4 ohms in order to stay clean. My amps in my space don’t deliver the goods satisfactorily in stereo mode.
Let’s do some history. As you know, the CS3 was set-up for bi-amping / bi-wiring. It separated the tweeter from the rest of the signal because the equalizer boosted the bass which included contribution from both the midrange and woofer, so they couldn’t be segregated to different amps. Audible improvement was gained by separating the tweeter. But the preponderance of users chose small SET or tube amps for the tweeter with no consistent way to gain-match the low frequency amp. Solving those variables would have required a different kind of dealer. Jim assessed that we didn’t have that expertise in the field to his satisfaction and removed the bi-amp /bi-wire option.
The scene is different today in that remaining Thiel users are likely to commit to getting it right or staying on the sidelines. It is tricky business, especially in the absence of clipping lights and with uncompressed and/or otherwise very dynamic music. Underpowering makes distortion and distortion fries drivers. Be careful.
