Do I need to bypass mixer preamp when plugging in external preamp?

[gene12586]

So the real problem isn't that the input isn't sensitive enough but that your PA isn't powerful enough. I wonder if you are expecting too much from the Stagepas. They are great PA systems for acoustic bands but could struggle if you are trying to overcome a loud drummer.

Right, but I'm almost always just using this for singing practice (just me singing, nothing else), and at most I will use it for just me and a guitar...