I believe the apparent loudness in the morning is simply due to expectations. We tend to sit down in the evening and get used to certain spl's, and tend to inch it up little by little until it pressurizes the room correctly. When hit first thing in the morning with it it is way louder than we would have thought. I don't agree that our hearing is therefore necessarily more sensitive in the am, just a matter of getting used to it. Same is true for concerts, etc. First song is perceived way louder than the last song of the night.
And with SP Tech speakers, louder doesn't mean distorted (assuming the rest of the signal path can handle it). My $.02