1 Subwoofer or Are 2 Better??

Sure two would be better. Four would be better still. It comes down to how much to spend and place to put them.
I bought one JL F-113 Fathom sub and it is awesome.
Again, two would be better... 2 costs twice as much, and I am not sure if I have the room for one more JL sub.
I use the JL sub with my Stereo system.

I also have 2 more subs (Outlaw Audio) for my Home theatre which is loacted in the same room with my 2 channel set up.

I think I still have a M&K 250 Watt 2-12 woofer sub if anyone is interested.

I found the Harmon paper interesting, although I think there was little new that I didn't already know, but it is a reasoned explication. Bottom line is that one well placed sub, often corner placed, is usually all you need unless your room is very large. As the series of papers notes, lots of unsubstantiated mystic in audio.

db

I also have a JL Labs Fathom 113
I don't feel I'm missing anything
although some year I may add another

this is in my HT room

my 2 channel room doesn't need subs