Dear Richard,
I hate to disagree but you are totally wrong.
I worked for Sound by Singer, in their glory Wilson years and I was in fact the top Wilson salesman in the country for most of that time, Mark Goldman would bear that out.
As an experiment I connected a REL Stentor to the Grande Slamms Singer had the Whamms but they were came and went, and low and behold much more bass and it totally integrated.
Singers big room was roughly 30 by 20 by 10 and even the mighty Grande Slamms which morphied into the Alexandrias, has difficulty delivering impressive low end into a room with that kind of volume.
As per the speaker is mostly sub woofer again not true, an active bass system will always produce superior bass performance as it is a closed system and many sub woofers employ thousands of watts of direct power to overcome the limitations of loss of sensitivity which occurs as cabinet volume shrinks, closed system means you can actively eq the woofer and produce a ton of output.
Also it is totally conceivable that this gentleman has the speakers setup perfectly and at 11 feet probably gets the best sense of depth with the most uncolored mid range.
There are a number of good subs which will match well, it also depends on how well they are setup.
Obviously the Wilson subs would be great however there are many others:
REL Stentor or Studio
JL Labs F113 two would be much more affordable tnan a Gotham
I would pass on Torus, very fast but not a lot of output
Escalante Unita hard to find but superb woofer lots of super tight output and very fast. Thiery Budge designed this woofer and he was the orginal designer of the WP by
the way.
I haven't played with the new Paradigm subs but they are supposed to be excellent.
Stay away from Velodyne not up to the task, slow and does not have the mega output of the JL.s
Newer REl's not as good as the older series.
I know Audio Feil is going to come calling but what do I know I was the top Wilson guy for many years and my customers included Qunintessential Sound and Tommy Boy Records, and I personally setup over 40 pairs of WP and a few Max, and Grande Slams in my day as well as personally owning both WP 3 and WP 5!