So your intent is to take some audio output on the sound bar and send that to the amplifier and then to the speakers outdoors - correct?
You must match the power amplifier to the speakers outdoors.
And likewise you must match the physical connections (sound bar to amplifierand amplifier to outdoor speakers).
Start by reading this tutorial from within this forum:
http/www.tomshardware.com/forum/58350-6-guide-audio-basics
Then work out and diagram what you believe is correct and post accordingly.
Do you have any specifications for the soundbar, amplifier, and outdoor speakers. That information will be helpful. Thanks.