Question I have a Koch amplifier. How can I make the G-Major / G-System switch the channels of my amp

The KC-50 Deluxe has two mono jack connectors. You need a standard stereo jack to 2 x mono jack (Y-split cable) to connect the G-Major´s "EXT CTRL" socket to your amp. On the G-system use SW1 or SW2
Relay 1Relay 2Channel
The Twintone amp with a stereo jack socket: Just connect using a stereo patch cable. The Multitone and Powertone amps, For this series Koch offers the "DJ-1". This is a small unit with four jack connectors. You can use a Y-split cable if you already got a DJ-1. The Multitone and Powertone footswitch has 5 switches (clean, crunch, lead, Reverb and Rhythm/solo). Two jacks on the DJ-1 are for the channels and the other two are for the reverb and rhythm/solo. You can also make a cable like the one described in the PDF document attached below. Information kindly provided by Koch Guitar Electronics.