Do I Need a Stereo to Mono Summing Cable/Circuit Between Pre-Amp and Equalizer for Subwoofer on Vintage Equipment?

Hi.
I recently picked up a Klipsch subwoofer to add onto my vintage stereo system. My configuration is as follows: Yamaha CX-830 Pre-Amp > ADC SS-315 Equalizer > Phase Linear 300 Amp. I currently have the subwoofer's input connected between the Pre-Amp's Pre-Out and the Equalizer's Pre-In using a Y-cable on the LEFT channel only.

My issue is that the Klipsch Sub (Klipsch R-120SWi) uses a Klipsch provided wireless module. This module connects via a single RCA jack (either full range mono or LFE). I would like to send both Left and Right signals to the Sub. I like picking up the signal before the Equalizer and adjusting the sound at the Sub.

I am concerned that if I use a simple Y cable to bridge the left and right channels between the Pre-Amp and Equalizer, I will effectively make all signals mono. I've been doing some research and stumbled upon a summing cable/circuit that uses 1K resistors like in this image found on the Parts Express Forum. Also, Paul from PSAudio talks about this on YouTube but suggests 10K resistors.

SummingCable.JPG


My question: Should I use a stereo to mono summing cable/circuit between the pre-amp and equalizer to obtain the mono signal to send to the subwoofer? Or, is there a better way to do this that I haven't thought of?

If it helps, here are HiFi Engine links to the components involved:
Yamaha CX-830 Pre-Amp
ADC SS-315 Equalizer
Phase Linear 300 Series Two Amp

Thanks
Ron