> headphone distribution box?
How "hot" does it have to be? Normal, or live music around drummers?
Does everybody get the same level? (If not, what you really want is a lot of individual headphone amps.)
The general plan is to use a loudspeaker amp plus series resistors. An 8 Watt 8Ω ohm speaker amp (cheap hi-fi) with a separate 27Ω series resistor for each ear will work fine up to 7 32Ω headphones (or up to 3 dead shorts).