Why is one sub not enough for your listening and do you know how to place the second such that it does not cancel out what the first is doing?

One sub might be enough. But that wasn’t my question . I know of several options in terms of placement of two subs, but none where one of them is located underneath a couch. 

Why did you buy the second sub? If it was simply to obtain more bass noise there’s your answer: move it around until you find the best place to induce haemorrhaging at the listening position. 

Because I got it used dirt cheap. 

Tell the GF she doesn't have to look at it, look at the screen instead.

 Walk the room, close to the walls, carrying a stack of Post-It’s and a magic marker. Play a thumping bass track. As you walk, you’ll notice spots with increased bass. Mark these spots with a Post-It. You’ll discover a few spots with even more bass. Mark these spots with !!!. The Post-It’s will be more or less regularly spaced around the room. These are known as “peaks”. Midway between peaks is a “null” where bass will be minimized. Placing a listener or SUB at a peak will increase the bass. After you become familiar with discovering peaks and nulls, you’ll be able to find smaller peaks and nulls in three dimensions throughout the space.

I don’t know anything about your decor, but you could hide SUB in a basket.

I’d sure try under the couch as a first location.

The other location suggestions are all good too.

Maybe better than under a basket, check out SoundSkins to make it less visible. Or make your own out of standard speaker cloth for a lot less money.

I hope one of the two Subs is a Gen 3, otherwise you won’t be able to use them in the same room in the Sonos software.