Why does my S/Pdif output only provide PCM out, although I have a DD amplifier connected and a (older model) beamer or (older model) TV connected looped on HDMI ?

If there is an apparatus without a (valid) HDCP key in the HDMI chain, then all outputs from the source must fall back to the lowest quality (usually SD for video and PCM for S/Pdif). These are rules stated by the Digital Content Protection LLC. The Leap S1 is compliant with those rules.
DTS and AAC are default Off, but can be switched on in the LEAP S1’s Device Preferences Sound menu.