funnily enough, we watched interstellar last night, on blu-Ray, and the sound mixing on it was appalling. We both really struggled to hear the dialogue. And that's through a decent Sony home cinema amp. If anyone hasn't seen it yet, don't bother, apart from the terrible sound mixing, the script is awful, and story full of holes. Biggest disappointment in a sci fi film since independance day.
But back on topic, I never had a problem hearing the dialogue with the Harry potters.