Ken, as to the "blending" that you speak of, this is exactly what the receiver's bass management is designed to do. For example, when 80Hz is set, the mains are rolled off(not sharply cut off)below 80Hz at 12dB per octave, and the sub is rolled off above 80Hz at 24dB per octave. So, it's unclear what the "harsh cutoff" you mention is.
Boominess is certainly not a characteristic of the EP500 that other users have experienced. As Jason and others have pointed out, this may have to do with your listening room, or more specifically the position of the sub within it. Another point is have you calibrated the levels of the sub and speakers with the automatic setup on the 3805(if you have the setup microphone)? Simply having the sub too loud in relation to the speakers can give an impression of boominess. The sub shouldn't be loud enough to draw attention to itself; the impression should be that it isn't working, but that the speakers are putting out more bass.
