]So, what does Darcy want in the way of a conversation? And with whom would he conduct that conversation? Evidently Sir William's small talk doesn't do the trick.

I hadn't realized that Sir William came up to him right after this, but you're right, this doesn't do it. I think Darcy made up his mind before he even left home that this was going to be awful as far as he was concerned and agreed to come along only out of respect for Bingley. Once there, he seemed to feel justified in his prejudgement of "country" people and chose not to converse with them. Darcy seems quite content to enjoy his misery amongst himself, so to speak. He appears to be indicting the entire assemblage for their pleasure of dancing and wondering why they would prefer this to conversation. I can only assume that he only wants to converse with those he feels are of his rank and class. Most of the conversations in which he contributes up to this point appear to be mainly at Netherfield and Caroline seems to be manipulating and setting the tone for most of these. Wickham tells Lizzie that, "Mr. Darcy can please where he chuses. He does not want abilities. He can be a conversible companion if he thinks it worth his while. Among those who are at all his equals in consequence." It would be interesting to know exactly what Darcy does like to talk about. :-)