Please ignore my DTS:X issue as i've resolved it. My receiver doesn’t disable the surround upmixing option to use the atmos speakers on non atmos soundtracks when playing a DTS:X soundtrack. It plays MA track instead as yamaha 2015 receivers cannot overlay a DSP onto an Atmos or DTS:X soundtrack.
Pressing straight allows the DTS:X track to play correctly. I was thrown initially as when a dolby atmos track is played pressing straight to disable upmixing is not required.