H/K makes decent amplifiers and receivers. But I dont' think they're in the same league as the high end Onkyo or the Pioneer Premier though. Velodyne, Infinity and Polk are in the same class as Boston. However, I think Boston's are much better. Especially their VR series for the home and the pro/Z series for the car. Polk's base is too boomy while boston is much tighter and more controlled. Infinity is somewhere in between.
I think speakers above $5k is more for the image than anything else. I doubt you can tell that much difference between a $5k speaker than a $50k speaker. I'm sure if you listen really closely, you might be able to pick out something, but I don't think the human ears are that sensitive.