My mistake; @tls49 is correct. There are indeed jumpers between the power amp and output 1 jacks. The rear panel photo I looked at yesterday wasn't clear enough to see that. No substitute for checking the original manual information. Apologies!
Regardless, have fun with your new 2600 and tell us how you like it. It's supposed to be quite the piece.
Regardless, have fun with your new 2600 and tell us how you like it. It's supposed to be quite the piece.