Actually, I agree with all of the observations here! On the question of using one or two subs, the room characteristics are important. In my experience, it is not just the presence of low frequency, but the also how the room is pressurized by the musical activity in the lower ranges. Since my full-range mains (Zu Druid) are somewhat light on the bottom, I've tried all of the above methods and am now most pleased with two subs. Incidentally,each placed just outside the mains and perched on low Lovan stands (this eliminates all hint of bloat and dramatically improves imaging for a fine, articulate bass). After experimentation, I've reverse-mounted and aimed the drivers toward the ceiling! In this way, the room is beautifully pressurized by two columns of low frequency sound. Standing waves are nearly impossible to find and the presentation is so very relaxed and natural. Being something of a diy person, my "twins" re-built M&K Volkswoofers. There is a top-to-bottom seamless presentation. Cross is set around 40Hz. The front end is exclusively tube gear.