Has any HNer participated in such a secondary sale? I think it could be informative to describe the experience, whom you dealt with, how a price was agreed upon, how your company discussed secondary sales, etc.
When secondary brokers have more buyers than sellers of a particular private stock, they come looking for you - and that's the time when you want to do your selling, not when people are freaking out and you're competing with others actively looking to unload their holdings.