@darwindesign I went through those docs on several occasions. They are well written and descriptive. Sadly I could not get it to work properly.
In essence I’ve configured: HDMI audio device output, 7.1, best match, allow passthrough for everything except DTS & DTS-HD. This does indeed transcode DTS to LPCM, and its read by the SB as multichannel PCM, but…
The DTS transcoded content (now LPCM) looses surround channels for some reason. The side and rear speakers are not used at all (some noise can be heard but it seems like very low volume stereo upmixing, bearly audible).
I have confirmed this using the DTS 7.1 speaker mapping demos (i.e. Dredd, and generic DTS speaker test video). If I play a raw LPCM 5.1/7.1 test video, native LPCM plays as expected on the SB; correctly across all speakers. 
I also tried to approach the problem from a different angle. Transcode DTS to DolbyDigital. Settings: HDMI audio device, 2.0, best match, allow passthrough for everything except DTS & DTS-HD, enable Dolby Digital AC3 transcoding. This works, surround channels are heard and the SB confirms the source is DD; but as said, I would like to obtain the audio quality of the source material, so LPCM is a preferred option, and this workaround is a last resort 
@mark22 I don’t want to go into any politics or future what ifs; the fact is that the home theater community still relies on BluRays as the best obtainable source format. Streaming services will never match the quality of BD or at least not for a looooong time (while I am still alive). Therefore I need a solution / workaround for TODAY. Also saying DTS will die is a speculation. Many movies are still DTS only, including the latest movie hit Oppenheimer.
@zatarra77 I have not dismissed the option of using an HDMI splitter, however, I have not found any that will still support all of the features of the TV. Not even the FeinTech 2.1 splitter would meet my requirements (4K HDR VRR 120+ Hz) These are mostly for the use case you had: an older AVR and a new TV; but in my case I have a 2023 model SB and TV, where only the TVs lack of DTS passthrough support causes headaches.
EDIT: Side note, when using DTS → DD AC3 transcoding, raw LPCM files are also transcoded to DD which is a shame (since my setup supports RAW LPCM passthroughs).