[jjd-uk]

I believe based on your explanation, this shouldn't have any bearing on my problem, so I am ok to leave it with Best Match then? (i.e. I couldn't "fix" it with setting anyway)

To always ensure correct channel layout then yes stick with Best Match, with Optimised because it uses the properties from the first track in a playlist for all tracks when continuously playing, then if first track was 2.0 then second track was 4.0 then Kodi would continue to output 2.0 from what I understand, it's however been a while since I last went into depth on this and fritsch is the audio guru who is best able to give the definitive answer.

To add to the above, I can't remember with 100% certainty with Best Match is whether the player process (audio sink) is always torn down between track transitions and restarted, or only when it sees the new file having different properties to what the player is currently using, this would maybe explain why you wouldn't hear much of a delay between track transitions if all tracks in a album or playlist have the exact same properties.