Hallo,
I hope I can help you with this informations for using the Helix with the Bogner ATMA. You just have to connect the ATMA to the Helix with a 6,3 mm Stereo Jack:
NO SIGNAL = ATMA KANAL 2 (CRUNCH)
2 (RING) = ATMA KANAL 3 (LEAD)
1 (TIP) = ATMA KANAL 1 (CLEAN)
Ulrich