I"m listening to greg brown...my name is bruce and the answer is within the design philosophy of the decapo i the answer is an unequivocal yes.If your listening taste requires sub 40hz than I would point you in the direction of a 3way design and never a sub.For home theatre applications a sub is a lot of fun but for critical listening when I mix down a string quartet I would not pull away from the cohered sound of the decaps by running with a seperate sub....
i must respectfully disagree here. imho, the best way to do 2-channel audio for music is to use a properly integrated pair of quality subwoofers, regardless of whether your monitor is two-way, three-way, four-way, full range, or whatever. this will always result in the best soundstaging, & most natural neutral presentation of music, be it chamber music, full orchestra, jazz combo, hard rock, or whatever.
of course, perhaps my views are a tad biased...

before this set-up, i ran these subs (in another dwelling) w/a pair of full-range (-2db at 20hz) thiel 3.5's. *everything* improved w/the addition of the subs: low end (doh!), imaging/soundstaging, dynamics, transparency/detail...
look at many mfr's no-holds-barred state of the art assaults on what they feel are the best possible sound transducers - many are monitors with subwoofers, straight from the factory...
ymmv,
doug s.