The description of Broken Sword: The Sleeping Dragon says:
"This is full "talkie" version of the game. You can turn the subtitles on if you prefer subtitled version."
Can you not have both options enabled, like in previous BS games? The voice acting is quite a landmark in the BS games so I'd definately want to have it on, but sometimes (at least in BS 1 and 2) the music and background noise (perhaps even the accent) overpowers the dialogue so much that I might miss a word or two, so I like to enable the subtitles as well.
Although probably not going to deter me from buying the game, I'd still like to know if this is possible without any kind of editing the game?

With the initial release of BS3 such a combination is possible (in fact, it's even set by default).
Since BS3 is fully compatible with modern PCs, I doubt GOG would change any executables, so I believe we could assume that a mix of subtitles and speech will still be possible.

In case you still want to know, it is possible to have both sound and subtitles on at the same time.

Thanks everyone.
Now I'll just got to finish Broken Sword 2 first!