Connecting Old stereo Receiver + active sub

[LoNc]

I have an old stereo reciver Pioneer SX-337 driving 2 stereo speakers.
Here is the Rear View:

Now, because I have a lack of bass cover , I decided to order Auna Active Subwoofer with this rear connections :

In this case i would have a 2.1 System.
Which is the best way to connect my old Stereo receiver with this Auna Active Subwoofer ( high level or RCA) ??

Thank you for your answers!

David

 

[Mousemonkey]

Take the feed from your speakers NOT the amp.

 

[LoNc]

So, you suggest high level connection ?

 

[Mousemonkey]

Your amp doesn't have a low level output so what other choice is there?