Swapped IC's
The 2 IC's on the IN/OUT daughter board are different. Don't swap them and insert them carefully in the right direction.
The pin 1 of the NE5532 is identified by a small recessed circle on the body.
Tips on how to solder the long 2x40 pins header
The main issue here is when you heat some pins for too long, they start to move because the plastic part which hold them together starts melting. The solution is to lay the header on a damp sponge while soldering the pins. The water in the sponge prevents the parts getting too hot.
