From the back panel each input pair (L & R channel) go directly to the switch, lets say input 1 left channel to the first outer tag pin after the mounting bolt and right channel to the opposite tag, input 2 to the next pair of opposite tags and work you way round with all you inputs.
The R & L switch outputs are the 2 inner tags, run wires from these to the R&L Inputs of the stepped attenuator .
Join all of your input grounds together for each channel with a tinned wire, run a wire to your start earth point and back to the Stepped attenuator grounds
The L&R outputs from the attenuator go to the Pre amp input L&R
I use a start earth point at the output Grd of the power supply caps so you would need 2 grounds from there to the ground on the amp board input
The output from the amp board go to you RCA outs on the back pannel
Note make sure that bolt on the transformer does not touch the top pannel or ou will get a short on your transformer
Hope this helps
IMG_0089 by Alan Towell, on Flickr
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