I don't understand the "how" of fast but will share my experience, for what it's worth. When I inserted a Supratek Syrah tube preamp into my solid state active system I was taken into another dimension. Very difficult to describe the way my amps were unleashed to do what they were meant to do. You could have knocked me over with a feather the change was so pronounced. I'll be happy to read to technical aspects of fast when the pros chime in.
What makes a sytem "Fast?"
What contributes most to the speed of a system.....the amp or the pre-amp?