how to hook up onkyo swk 50 subwoolfer to sony dh550 receiver

Solution
If you have a Sony STR-DH550 5.2 channel receiver you can use either subwoofer output.
In most receivers when you plug in headphones it turns off the speakers so connecting a sub to that may not work.
You could connect a speaker to line level converter in parallel with the speakers and connect one of the output to the subwoofer.
It seems there aren't many analog outs on that Sony. You need an analog out to go to the subwoofer.

What you can do is come out of the headphone output with this and go to the subwoofer.

https://www.amazon.com/InstallerParts-Compatible-Amplifiers-Instruments-Microphones/dp/B0759YCMFF/ref=sr_1_4?s=electronics&ie=UTF8&qid=1521054111&sr=1-4&keywords=1%2F4%22+stereo+to+RCA

The Sony looks like it has a volume control for the headphones....so you don't want this too high or too low. I'd say about two thirds up would work OK.
 
If you have a Sony STR-DH550 5.2 channel receiver you can use either subwoofer output.
In most receivers when you plug in headphones it turns off the speakers so connecting a sub to that may not work.
You could connect a speaker to line level converter in parallel with the speakers and connect one of the output to the subwoofer.
 
Solution