Both!
Any info going to surrounds lower than 120 goes to the sub and for the center channel, anything below 80 goes to the sub.
H/K use to have what they called variable quadruple crossover which let you assign different xo's to various speakers. It was my first rec'r and since then every subsequent rec'r has not had that handy feature which I miss.
My understanding is that the LFE signal includes frequencies up to 120 on it's own plus anything you crossed out of the other channels. I feel like I must have missed the true question as I'm pretty sure you know this stuff.