The Atmos up mixing add 2 height channels regardless if you have a 7.2.4 setup. so 5.1 gets up mixed to 5.1.2 that's it, the rest of the channels are blank. If you turn it off then it's 5.1 with the rest blank. The output signal though is whatever you max speakers are set to. So you can't upmix in receiver unless you set it to Dolby or Dts 5.1. Lpcm has a similar problem with blank channels on 5.1 tracks as there is no up mixing to 7.1.
TV-Sony Bravia KD-65"A1, Pioneer SC-LX901 7.2.4 ATMOS/DTS-X, Polk DSW 660*2, Polk RTi A7*2, Pol Csi A6, Polk RtiA5*2, Polk Tsi300*2, Polk TSX 220B *2, Polk OWM 3*2, Zappiti-4kHDROne, Oppo UDP-203, XboxOneX, PS4, Oppo BDP-83, Darbee DVP-500s, ZidooX10, Sony Bravia HX925 55"