I've seen American Red spruce that is as low in density as any European or Engelmann spruce. You have to hunt a bit for it, but it exists.
Back in the 30s, as they were running through the last of the old growth Red spruce, the Martin company used to source it from several different places. They got some from the mountains of Western Virginia, iirc, and called that 'Appalachian', but they got more from upstate New York, and that was 'Adirondack' spruce. It's the same species: Picea rubens. The stellar reputation it has is due to the fact that Martin supposedly made their best guitars in the 30s. Since they were using (mostly) 'Appalachian' spruce and Brazilian rosewood, those became the 'magic' woods, responsible for the fine tone of the guitars of that era.
Recently somebody pointed out that Martin, like all the other manufacturers, was working flat out through the 20s, but when the Depression hit they cut 'way back. Naturally, when they laid off workers they kept the best ones, and, of course, those remaining workers did their best work so that they would keep their jobs. There was no difference in the wood from the 20s to the 30s, but maybe the 'average' worker was better? To me that's a very plausible hypothesis.
"I have read that adirondack has the highest volume ceiling. "
That property, which is often called 'headroom', seems to be a function of the density of the wood. Since the energy in a plucked string is limited builders generally try to make the top as thin and light as possible. The limit for that is established by the stiffness necessary to keep the top from folding up too quickly under string load. Denser wood tends to be stiffer at a given thickness, so you can work it down a bit to get the stiffness to be right. However, because of the way stiffness relates to both density and thickness, the denser top will tend to be heavier at a given stiffness. This makes it a bit harder to push, but also harder to over drive. For various reasons this sort of 'headroom' seems to be less of an issue in Classical guitars than it is in steel strings, and particularly in the scalloped-braced Dreadnoughts that Martin originated.