I think pregnant pause is a better phrase to carry the definition "a meaningful silence." A resounding silence is notable not for its meaning, but for the lack of applause or acclaim. (Rolig put it very well, IMHO.)
Mia, thanks for listing all these. We have had some really interesting discussions today!
nach, what I think Mia meant by "meaningful" was that there was some specific meaning to be taken from the silence (unlike the silence, for instance, at a gravesite -- which is appropriate silence). Meaningful silence is a silence that actually says something (either positive or negative) and is not an expected silence. What is being "said" by the silence has meaning beyond silence, in a big way....Eh?
I think the idea in the oxymoronic phrase "a resounding silence" is that something that was expected to meet with praise or at least to generate interest in fact received no response at all, not even a negative or critical opinion. So if someone says, for instance, "His second movie was met with a resounding silence", this does not mean that it got bad reviews, but that it was essentially ignored. The meaning of such silence is debatable, though I would say the usual implication is not that it expresses a negative opinion, but that it expresses an inability to understand or evaluate something.