He can run them as is, if he doesn't mind listening to silence. As you said, he can also hook-up a pre-amp or a graphic equalizer, but he would still be listening to silence. In either case, he would still need some kind of music source to listen to. That might determine what else he needs.
My most minimalist system uses just an iPod hooked to a Sansui power-amp
to Polk speakers. My other minimalist system uses just an Audiotron
for a source, hooked up to a Phase Linear
power-amp and Quarte speakers. Since all of my music is on a network, this is all I need. I've considered putting a graphic equalizer in the loop, but I don't need a pre-amp.
If I had multiple sources, needed record capability, or wanted bass/treble control, I could use one of my graphic equalizers as a pre-amp. Besides the ability to have more sources, a pre-amp doesn't offer anything I would use.
I have one system with a pre-amp, and that is because it needs to support two turntables, a tuner, a reel-to-reel, an audiotron, and a computer.