Can the Denon AVR-S570BT drive the KEF LS50 Meta?
The LS50 Meta is 8 Ω nominal, inside the 6 Ω rating of the AVR-S570BT, but it dips to 3.5 Ω. Fine at normal volume. Go easy on long, loud bass.
Everyday listening is fine. The nominal impedance of the KEF LS50 Meta is inside what the Denon AVR-S570BT is built for. The dip below that rating is a caution, not a thermal overload.
At 3.0 m in a typical room, the stereo pair reaches about 99.9 dB. The second speaker and the room each contribute roughly 3 dB, which is the usual allowance for home listening. That sits 5.1 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 AVR-S570BT is rated 70 W into 8 Ω, and the LS50 Meta works out to about 85.0 dB for 1 W at 1 m from the sensitivity the maker actually published. Nominal impedance is 8 Ω.
The published minimum impedance is 3.5 Ω.
Do not declare the amplifier unsafe because of the dip, and do not ignore it during long, loud sessions: sustained bass asks for more current than the nominal rating describes. A more powerful amplifier does not erase a dip. It only helps if the current one is running out of voltage and clipping.