[noggin]

Multichannel PCM in case you happen to playback audio that cannot be bitstreamed like 5.1ch FLAC, AAC etc. so they will be decoded and sent out as multichannel LPCM. What you have set in the Passthrough options, will be sent without decoding.

Thanks for reply.  I've kept that setting HDMI Multi Ch PCM

Can anyone confirm i have it rest setup good.

I enabled passthrough for my avr
denon avr x2500h

i enabled all the options dtt,dts hd etc ( not sure about digital plus)

Not done anyhing else as unluckily the servers are down with coreelec so not managed to do much else.

Thanks
Sim   

If you have an AVR X2500H and a 5.1 or 7.1 speaker set-up (or equivalent with Atmos height speakers) then set your Number of Output Channels to 5.1 or 7.1 etc. (whatever your speaker configuration is - though you may want to leave your .1 in even if you don't have a subwoofer to let your AVR do bass management rather than Kodi).  That will ensure all non-passthrough formats like PCM, FLAC, AAC (*) etc. are decoded and to 5.1 or 7.1 PCM.

For bitstream formats - enable passthrough and enable passthrough for AC3/Dolby Digital, E-AC3/Dolby Digital Plus, Dolby True HD, DTS and DTS HD. This will mean that all the passthrough formats will be passed through (i.e. bit streamed) untouched for your AVR to decode. (Your AVR will also indicate the bitstream type)

(*) Technically AAC can be carried over HDMI as a bitstream - but it's never really been implemented in Kodi (and support for AAC-over-HDMI is - or was - very rare outside of Japan)