You can operate a maximum of 7 speakers with the Denon AVR-X1500H, plus an active subwoofer. This means that the Teufel mentioned with 5.1 plus two Atmos speakers (e.g. the Teufel Reflekt) is within the specifications and can be operated in this way. Whether this works/sounds well is, of course, another question. The Atmos Reflekt story is, by the way, quite strongly dependent on the room and the set-up.
Another thing I noticed: Teufel also combines the System 4 THX with an Onkyo reciever. On paper, it has considerably more amplifier power than the Denon X1500H. I don't know what the efficiency (sound pressure per watt) of the Teufel is, but because of the powerful Onkyo, I assume that it is not as high. But all that only matters if you want to listen loudly. Room volume in a block of flats will probably be no problem for the Denon/Teufel combination. Bleeding ears would probably not work.