I had to take a long break from this project while I assembled some PC boards to replace sold inventory. With that mostly done I've begun the layout.

Wet Dry Mix Add Parallel Processor PC Board Layout
The board is the same size as the MS Mini which is 3.7 x 2.75".
Wet and Dry inputs are on the left.
IC5 and IC6 buffer the Mix/Add pot or stepped switch.
IC7 and IC8 is the summing amp with optional variable make-up gain.
IC9 and IC10 buffer the Mixed output.
RY1 selects Mix/Add.
RY2 provides soft bypass functionality.
J1 and J2 select the bypass input source which can be either the Dry or Wet input.
J3 and J4 when open allow a gain trim pot or switch to control make-up gain.
I need to tweak the layout and check it a bazillion times and conform the schematic to the layout but the hard work is done.
It pays to get away from it for a few hours and then look at it over and over.