Hello, my Onkyo A-9010 amplifier does not have a dedicated subwoofer output, but it has an L/R line out. Subwoofer Klipsch R-100SW has an L/R line in. Can I use a double RCA cable (2x in, 2x out - as in red to red and white to white), or how can I connect the two devices? Thank you!
The line output is fixed so the sub level won't vary when you change the volume of the receiver.
You will need a speaker to line level converter. That would be connected to the speaker terminals in parallel with the speaker wire.
Your speakers will be operating full range and won't play any louder than they could before you connected the subwoofer.