Hmmm. I can’t see any difference in the logs between LPCM and DTS decoded to LPCM. In each case you get
2023-12-13 19:08:59.143 T:774 debug <general>: CActiveAESink::OpenSink - ALSA Initialized:
2023-12-13 19:08:59.143 T:774 debug <general>: Output Device : vc4-hdmi-0 (vc4hdmi0)
2023-12-13 19:08:59.143 T:774 debug <general>: Sample Rate : 48000
2023-12-13 19:08:59.143 T:774 debug <general>: Sample Format : AE_FMT_S24NE3
2023-12-13 19:08:59.143 T:774 debug <general>: Channel Count : 8
2023-12-13 19:08:59.143 T:774 debug <general>: Channel Layout: FL, FR, LFE, FC, UNKNOWN1, UNKNOWN1, UNKNOWN1, UNKNOWN1
2023-12-13 19:08:59.143 T:774 debug <general>: Frames : 2400
2023-12-13 19:08:59.143 T:774 debug <general>: Frame Size : 24
So the difference must be coming from how Kodi is interpreting your set-up for the DTS-LPCM conversion. The HDMI audio device reports only 6 channels, and the audio capabilities in the EDID has two LPCM devices - a stereo one (?TV) and a 6-channel one (soundbar). That suggests the soundbar is not inviting any more than 6 channels. But Kodi doesn’t know that. I’m guessing you will get better results by setting audio output in Kodi to 5.1 so that Kodi does the downmixing and doesn’t get confused. Dolby should still pass through OK.
Note that when it says Channel Count : 8, that’s a limitation of HDMI - it can only be set for 2 or 8 channels. With 3-7 channels, the unused ones should be muted.
Let us know how you get on.