Can't comment on the Stereo/Mono question, but REL is certainly the most musical, and coherent sub in my experience with 5 different brands. Others might impress for a short listen, but over time the Rel sounds more natural when dialed in. I like smaller drivers because I like to hear more pronounced plucking of the strings over maximum bass energy, but that's a personal taste thing.
Monitor enthusiasts: musical subwoofers?
What makes a musical sub musical? I am considering the addition of a sub to my monitor-based system, but for the most part I find subs intrusive and difficult to "blend". In selecting a sub for use with a monitor type of speaker (rather than a large floor stander), what do you prefer? Stereo subs? Multiple smaller drivers? Any thoughts/suggestions/philosophies appreciated, Jb3