I'm sure he could, too, but as yet, no headphone amp is intended to do that. There are some speaker amps, maybe (the Halcro TOTL [don't know what it's called] and the Musical Fidelity kW are the only two I know that are designed to be able to "drive any load", and the few ribbon owners I know are usually fond of the higher-watt Krell monoblocks [FPB250's?]). EDIT: See?
But I didn't mean to infer that those two statements are related -- he didn't say why he wouldn't sell the headphone ribbons separately, and I didn't ask.