What is DTS:X?

In plain language

DTS-HD Master Audio is lossless multichannel audio, the DTS counterpart to Dolby TrueHD. DTS:X is object-based, the counterpart to Atmos: sounds placed in space rather than assigned to channels, without a fixed speaker layout requirement.

DTS:X IMAX Enhanced appears on some discs and receivers as a further variant.

Why it matters in your setup

Which format a disc carries is the studio's choice, not yours. A system that handles Atmos beautifully but has DTS support missing from its advertised capabilities will fall back on every DTS title — and since roughly half of releases use DTS, that is not a rare event.

DTS support is advertised as its own set of EDID flags, quite separate from the Dolby ones, so it can go missing on its own.

What the DR HDMI 8K does with it

The DR HDMI 8K reports DTS capability separately for both sides of the link — the Audio DTS line for the connected sink and for the EDID the source reads. In the audio flags, DTS-HD MA has its own control with a sample rate and a DTS:X IMAX option, and plain DTS its own on/off. If DTS titles behave differently from Dolby ones, that is the first place to look.