Thanks for everyone who has answered questions! :thumb: I have been away from the forum lately (My family is about to grow!) or I would have tried to be more responsive. I've got a few DIY projects coming up so I'll be around more for the time being...
As mentioned, the project is meant to be used with a mic pre for makeup gain. The preamp I/O connection points allow you to bypass the mic pre makeup when engaging bypass to route 1/2 to the main outputs. We added this to the board for v2 because w/ v1, if you bypassed and still have the make-up gain turned up, you got a big (possibly even speaker damaging) surprise! I'd still recommend watching the volume when switching in/out of bypass in any case. The other option is to leave the bypass out entirely, in which case the jumper that Holger mentioned is ideal.
Good luck w/ the board, let us know how it goes!