Carlos
Here's an comparison how the 2 speakers, i.e. Thiel CS 3.7 and B&W 802D behave electrically with an amplifier.
Look the 3.7 measurements. The Solid Line is the Impedance while the dashed Line is the phase behavior.
The Impedance of the 3.7 is generally low, with the power band sapping at 3 ohms most of the time. At 60Hz, the phase is 40 deg capacitive and the overall phase then improves over the low impedance power band to better status, hence relieving somewhat the amplifier.
Nevertheless, 3.7 will require a high-current amplifier which should be adequately stable when phase starts to play up. 3.7 also likes to be driven hard, so needs power. The ML-333 which is a 300 watter will basically be outputting greater than 600 watts when hooked to the 3.7. This is good enough to drive the 3.7 well.
B&W 802D's electrical impedance & phase behavior is quite different from the 3.7. The 802D's impedance sits around 3.5 ohms most of the power band from 70-700Hz hence sapping power out of the amplifier while the phase is jumping about, playing gymnastics from 50 deg capacitive to 50 deg inductive, hence really creating a turmoil to the amplifier and throwing it about.
Due to this problem with the 802D, and also the 801D and 800D, most demanding installations worldwide biamp their speakers, with 2 identical high-current, high power amplifiers in a vertical arrangement. This allows the speaker much effortless drive, the amplifier in-turn is relieved & happy to drive the drivers, and provides the true sound which B&W created that lesser setups cannot achieve, so customers blame the speaker as not satisfying enough for the money. These B&Ws require high quality amplification and the moment you give them that, they deliver the goods big time!
Since you own the ML-333, I suggest its is ok to start with the 802D. In time, you may look into sourcing another 333 and park it in a vertical biamp arrangement, i.e. stereo amp next to the each speaker, and this would facilitate independent drive to low freq / mid-high freq while also monoblocking.
I guarantee if and when you get to this situation, that speaker will overtake a lot of speakers in its way. The dynamics will "frighten you".
Cheers! And have a good day!
P.S. Just for your comfort, B&W UK factory Demo rooms before they acquired "Classe" used to demo their upper level speakers like N800/N801/N802 with ML electronics, mostly the 33 or the 33H. I've also seen the 336 x 2 in some cases.