negative output zens to subamp

[traw]

If connecting a speaker with subamp for bass with high level inputs and using a zen9, would one connect the amp output - to the highlevel in red, amp output + (ground really) to the black of the highlevel input then do 180 phase ship on the bass amp?

[Nelson Pass]

The subs usually have a "hot" and a "cold" and the cold is almost
always ground, so you need to connect it to ground even if it
is the "+" terminal at the output of the Zen. Most subs allow
switching of phase, so this isn't a problem, otherwise you can
flip the phase to the main speaker in the wiring.