Two Subwoofers Connection Advice

What @joshua43214 said. 

I had a Marantz receiver and ran two subs.  If I recall correctly, the two sub outputs were a single mono output that was split inside the unit to offer two sub "outputs".  Your best connection will likely be a single RCA cable into the LFE or mono input on each sub.  Good luck and cheers.  

I was still trying to set up dual SVS stereo subs for the first time. A week into the process I was having  no success adjusting both subs at the same time to identical settings. I had reached a high frustration level while keeping my blood pressure under control, but the sound was a confused mess. I'll sleep on it.

The next morn in the shower (please don't try to picture it) it came to me that trying to set up two subs at the same time was a fool's errand. I decided to run L&R ICs to each sub and set it up individually to the mains and room. Before embarkimg on this path I called SVS support for their experience. She was unresponsive to my plan of single sub setup but gave me two useful pieces of advice:

1)Because of the room the settings on the two subs can vary wildly. MY room is VERY different L vs R!

2)When you remove one interconnect when reurning to stereo you will lose 6dB of sound. Good to know!

First I ran both ICs to the R sub which was in a position I had been usimg for a single sub for 20+ years. In less than 10 min I achieved perfect intergration thanks in part to SVS's app, the best app on the planet. I set those perameters to a preset.

Next I ran the ICs to the L sub, forgot the previous settings, and duplicated the process. 10 m later the sound was extremely pleasing. I set the preset and compared notes. Yes, the two settngs varied wildly!

Then I wired the subs in stereo and added 6bB of gain to each sub. I put on some music and was greeted with one of the biggest and most profound improvements my system has ever had. It was  worth the journey for the valuable knowledge and profound beauty dual subs have given me! Go dual as soon as you can!

After a day listening to the above setup, I was not confident that I was getting the max out of my system. On Sun I was blessed with horrible weather and decided to tear everything apart and do my first sub crawl.

The chief impediment to doing this is long enough interconnects to run from the preamp to the sub at my listening chair. I had two Rolls Mini Route 3 RCA switches that I used to connect two 5' ICs together in line and they just reached. I played Superbass live, Telarc, track 1 on repeat through the sub only while I crawled my room multiple times until I understood what I was hearing.

I learned that the place I had been using a single sub for 20 years was sitting in a null. The back rear corners were a boomy mess. And there was a spot on each side wall halfway down that I found uniquely articulate with singing bass. No other spots compared. I had been my own worst WAF in setting the subs where I wanted them for convenience, instead of letting the acoustics run the show. That is why I have a dedicated room, isn't it? It's always fun to be humbled with new knowledge!

I set the subs in the room's sweet spots and indiviually calibrated them using the method written above. When I turned on music I was startled by how IMMERSIVE and beautiful the sound was. The bass integrated the mids and highs for more color than I thought my speakers could give. I no longer feel a need to do another setup.

Am I done? Not unless you are extremely good or lucky. When listening to music that evening I found a need to experiment with the gain (oh so easy with the SVS app) moving each sub up or down a couple of dB until I achieved perfect balance between the lows to highs and balance between the channels. It was easily evident when this happened. It was so relaxing and natural.

I temporarily moved two recliners into the rear corners to stop the boom. It worked. I will wait for another rainy day to dig into REW and search for peaks to be tamed. I am too tuckered out to predict when that will happen. Meanwhile I am patiently awaiting the delivery of the new ICs and PCs to arrive in the face of a winter storm!