That's the norm, yes. The amp he's building for me will feed the preamp outs all the time. This won't affect the performance at all, Mikhail assured me, since the preamp out will only handle very easy loads.
It's more of a novelty than anything, but it would allow me to drive a pair of open headphones combined with a low-crossover sub for the deep rumbling if watching a movie or listening to organs (I like to feel the deep rumbling in my guts).
Yeah, you heard me. Some people want the option to add a woofer to their headphone system.