All right, a common question.
Is it necessary to drive excitement through pose readers? Shouldn't it be animator controlled? Does volume preservation happen without it (poissons ratio, compression resistance)?
It is not necessary to drive excitation through pose readers. It can be driven multiple ways. One thing we used to do which is pretty straightforward is drive a base excitation based on some distance between points or "pose readers". In the animators scene you can give them controls that end up feeding into the excitation at bake time, either override base excitation or add to it. Some muscle firing will never be figured out by an automatic system as it is more so performance based. Is the character flexing to be threatening? Is he carrying a very heavy box?
Volume preservation still happens without it.