Why magic at 80 db?

It may not be your speakers. I have owned Salks before (HT3's) and didn't experience this phenomenon - but have in the past.

It actually turned out to not be the speakers.

This may or may not be your amp - but I would look there first. The reason I suggest this?

Some amplifiers really "come into their own" / "sing" / etc at a certain level. This isn't just volume, but amplifier load as well as matching the amplifier with the speaker. If using a tube amp, try the 4 ohm taps instead of the 8 ohm taps. Perhaps try another amp?

There are some amps that excel at low level details/dynamics - for instance the six moons (.com) review on the KwA-150. Some amps deliver great current and control at lower volumes. Other amps need to be "goosed" a bit before they open up and sound more effortless.

Just another angle of thought - as I have run into this phenomenon in the past as well.

Been hanging out with a professional sound engineer off and on, tweaking
my speaker placement, talking trash and such -- and it turns out that the
golden number where virtually all music is mastered in the studio is at
83db. He can pick it out be ear, just magically knows when it is at the right
level, as that's where it hits the grove and does what it was recorded and
mastered to do. (And must admit, the amount of information he can hear
and explain about the mastering and mixing decisions behind any given
track is astounding). But if it sounds like it all comes together and the
magic happens just north of 80db, that's because it was mixed that way
very much on purpose. Short version: all our collective fascination with
hardware permutations notwithstanding, i suspect this one is pretty much a
software issue. (Personally, I find 83db to be rather loud in my room,
louder than I listen 90% of the time. Feel that I get all I need from lower
volumes -- but, must admit, once you spend some time at or around that
baseline level where things were mastered, it starts to get awfully
addictive....).

yeah, I noticed that too on just about every system I have put together. I think it is a major challenge to put together a system that really comes to life at DB less than 80. So between 80 to 85 is where I mainly listen. From a hearing protection standpoint, am I still at safe levels?

Looking back at my post above, occurs to me that I may have stumbled into an old chicken and egg conundrum: do things sound best at just above 80db because they were mastered at that level to sound their best, or are things mastered at 80db because that's just inherently where things sound their best to the human ear over a prolonged period? Dunno, but I suspect ultimately a mix of both. But, either way, seems like a known factor.

To support Mezmo's observation: (http://www.digido.com/honor-roll.html) Also- some systems take more power, before they, "come alive" than others. How many hours do have on your speakers(are they a recent acquisition)? Most driver compliances take time to break in/loosen up, before they sound their best and most dynamic.