and your guitar you would run through a direct box, and then take the direct box output and put that into a microphone >input.
maybe all that extra gear isn't needed tho' Some small mixers have a dedicated instrument input these days. Also consider that the output from the guitar, assuming it's battery powered, is likely to be able to plug into a line input. (low impedance) That will probably work. It if doesn't then some kind of pre-amp will do the trick, and that could be any effects pedal that isn't being used in true bypass. You can certainly try plugging the guitar straight ito a mic input, and use the volume control on the guitar to stop it overloading. ( but only bother if putting in the line input is way too quiet) Going from a mixer to the Boomerang doesn't really need a special box, the Boomerang is almost certainly designed to work with a reange of inputs, not just guitar....but do turn down the mixer output volume as necessary to avoid distortion. andy