Im aware its an old system but its currently what i have. But im attempting to create 4 speaker surround sound using this receiver, only issue is my rear speakers dont output any sound. Im not sure what information is needed but please feel free to ask away. Any help is greatly appreciated.
The amount of rear channel output will vary with the source and content.
You need to select the appropriate surround mode on the receiver. Dolby will give you the most accurate amount of surround sound. Other modes will likely product more constant surround sound. Use what you prefer.
You can get the owners manual here. https://www.hifiengine.com/manual_library/sony/str-d515.shtml
Go through the set up to adjust the levels of the rear speakers. Then you will know that if there isn't anything coming out of them there isn't supposed to be anything coming out of them.