So I purchased the parts for two kits and put the amp together but I'm trying to figure some things out.

1. I am a bit confused about wiring configuration for two stereo kits.
I've tried layering the output wires from the 2nd kit onto the first one and they sound great but I'm not sure it is the ideal setup.

2.  I am getting feedback when I turn the volume from 1/2 to 3/4 then it disappears at full volume most of the time. Is this the pot or could it be the way I've wired the circuit?

Any suggestions, comments or criticism is welcome.