The first thing you need to remember is that the Boomerang (along with most loopers) operates at instrument levels, not line levels - when referring to signal strength. If you are running your signal from a mic preamp to the Boomerang, that signal is at line level, and is too hot for the Boomerang. It will distort and clip your sound. If your acoustic has an instrument output, then that signal is fine for the boomerang. Once all your signals are at instrument level, then you can get a simple A/B-Y switch (Lehle makes an excellent one) and run whatever one you need into the Boomerang.
I use my looper for saxophone, and I have to lower my signal from the mic preamp output from line level to instrument level. I do this with a "Re-Amp" box. Mine is a passive unit made my Radial, and it sounds great. I love that it is passive, and does not color the sound at all. Now that my signal is at instrument level, I run it through a compressor, then a couple pedals, and then into the Boomerang. Then the signal goes to an Eventide Space reverb unit, and the output there is stereo. I run the stereo instrument-level signal into a Radial JDI Dual stereo direct box, and that goes to a stereo mic preamp and into the PA rig from there. Below is a link to the image of my rig.
Just keep track of the levels of your signals, and make sure they are all the same. Reamp your line levels first, run instrument level signals through your pedals & boomerang, then bump them back up with a direct box and a mic preamp and you're good. I hope this helps.