Are 40 watts enough? NAD C 316BEE V2 with the ELAC Debut 2.0 B6.2
Yes. The C 316BEE V2 into the Debut 2.0 B6.2 stays inside the amplifier's impedance rating. At 2.5 m the pair reaches about 99.8 dB in a typical room.
The NAD C 316BEE V2 is a fair match for the ELAC Debut 2.0 B6.2. The nominal impedance is inside the amplifier's rating, which is the condition that matters.
At 2.5 m in a typical room, the stereo pair reaches about 99.8 dB. The second speaker and the room each contribute roughly 3 dB, which is the usual allowance for home listening. That sits 5.2 dB under a 105 dB theatrical peak, so loud film moments are where an amplifier with more voltage starts to matter.
Behind that level: the C 316BEE V2 is rated 40 W into 8 Ω, and the Debut 2.0 B6.2 works out to about 85.8 dB for 1 W at 1 m from the sensitivity the maker actually published. Nominal impedance is 6 Ω.
An amplifier rated above the speaker is not automatically dangerous. Clipping from too little power is what sends extra energy into the tweeter. Keep the volume clean, and treat an unpublished impedance dip as unknown rather than as a guessed fraction of the nominal.