Thanks for the link, much appreciated.  It might be higher end than I need, but I can take a closer look.   (They're actually called insert earphones—I mistyped above—and here's a link.)  

Thanks for the reply.  I'll look into speaker amplifiers.  (The earbuds being used are specially for high levels—the specs in my original post are from their data sheet.)  

The high volumes are for use with a very low duty cycle signal as part of an experiment.  No ears will be harmed in the amplifier's use. :)  

I'm looking for a headphone amp capable of driving 50 Ω earbuds at up to 5 V rms / 20 V peak (1% duty cycle).  Any recommendations would be terrific.  It doesn't need to incredibly high fidelity—I'm aiming for the low hundreds of $, if possible.   Thanks for reading!