That is an eq that goes in your head.
^No, it's used to increase your guitar's signal to line level so it can drive a power amp or pa which in turn will drive speakers.
it brings your guitar to a line level as well as giving it tone (distortion, EQ). after being brought to a line level, you can put it into a power amp and then a speaker cab, or into a PA system, or into headphones or recording
Keep in mind, the Randall preamps you're looking at are built for the MTS, Kirk Hammett, and George lynch heads. I believe they also work in an Egnater head as well.