It’s in the PS5 settings. You can adjust speaker position as well.
Yes, but it's for DTS and Dolby Digital audio, like PS4 have.
New Tempest Engine is currently working only with the headphones (at least that was the plan and I saw no other info till now).
Although in the end the sound should still be in DTS for AV Receivers to support it and obviously Sony don't want to license Atmos.
I guess Tempest engine will be about generating DTS sound output for object-based sound.
I don't know how it'working now in games - should be similar technology, but maybe less complex.