Jeffcwrote:
I what to buy two pairs of RF wireless headphones so that two people
can listen to the same output at the same time. I'm guessing these
things come tuned to different frequencies which would mean it
wouldn't work.
How can I get around this

You could use a model with adjustable tuning.
Ex: Advent AW770 (900MHz) Very nice.
Used in several recording studios (according to
their engineers on this newsgroup. US$100

Both transmitter and headphones/receiver are
tunable so you could transmit several (4-6?) different
channels and use any number of receivers.