All right... I've now beaten my computer repeatedly with a stick, while mumbling arcane spells and uninstalling/reinstalling various components - I've even fiddled with the Defiler Pack mentioned in a previous post in this thread (although that alone didn't work)...

...and I am happy to report that somehow (though I'm fecked if I know which part of it did the trick) I am now able to play these files without problems.

However, this does not alter my position that the format is unusable for a general release, because a disproportionate number of users will be unable to view it. It must be considered a supplementary format, for connoisseurs.