Eliezer - I also think the talk of 'internal narrative' is potentially misleading, since it brings to mind the auditory qualia or phenomenal feel of your thoughts, when really (I take it) you just want to talk about the underlying neural processing.

I won't address the rest (it can't be an empirical question what's logically possible, etc.), other than to agree that we have some very deep-rooted disagreements here.

One final point bears noting though: my own fondness for the combination of zombies and epiphenomenalism may have inadvertently misled you about the state of the debate more generally. The two positions can come apart. So note that your arguments against epiphenomenalism are not necessarily arguments against the conceivability/possibility of zombies. (The latter view does not entail the former.) See Chalmers' paper on Consciousness and its place in nature [pdf] -- esp. the discussion of 'type-D' and 'type-F' views -- for more background.