5.1 AC3 encoding *without* passthrough? any way to do it?

Hi,
Recently moved to a new 4k setup and bought an Odroid N2+ to drive it.
I used to set kodi to send PCM direct to my sound system over HDMI but it doesnt support 4k HDR passthrough, so for best picture I’ve gone direct to TV and using ARC back to sound system.
With ARC - no multichannel PCM.
Kodi AC3 encoding works great, but I have to enable passthrough for it to work, meaning with AC3 encoded content I lose Kodi volume control, dynamic range compression etc. Volumes are all over the place.
Is there any way I can force Kodi to decode/re-encode ac3 source files, or have Kodi send multichannel PCM and then have CoreElec transcode that to AC3? Any add-on? Any system workaround? Any way to do it via ALSA or Pulseaudio?

Would appreciate any advice or help.
Adding a HDMI splitter is a last resort.