Headphone distribution amplifiers can be found from musician sources such as Musician's Friend. Multiple-output headphone amps are used in recording studios for monitoring the backing tracks while laying down your parts. If you do go shopping for a headphone amp, be careful. Some things called "headphone amps" are guitar amplifiers that happen to play through headphones- not what you're looking for.

Seems like overkill to me, though. Dionysus said that he plugged his headphones directly into the line-outs and it was fine. Whenever I tried to do that on other consumer electronics devices, the level was too quiet for me, but I haven't tried the Empeg and perhaps it's different.

-- Tony Fabris -- Empeg #144 --
Caution: Do not look into laser with remaining good eye.