Jonsher, as always there are tradeoffs when using one or two subs. Provided the subwoofer cabinet is well braced and has no resonances and that you blend it well with the satellites, you can use a single subwoofer and never notice its contribution to the sound. I have done that with RELs many times for myself and for friends, even with difficult speakers like Quads. I am sure it can be done with one DD-15.
By the way, bass foundation is only one of the advantages or subwoofers, the other is improved soundstage due to the ambience cues that were previously hidden in very low frequencies. You can read more about minimonitors and subwoofers at my blog here (scroll down). Both articles are targeted at new audiophiles but the basics are sound, I believe.
As you will see there, I am a fan of small high-quality monitors and subwoofers instead of floorstanders at a similar price point.
By the way, bass foundation is only one of the advantages or subwoofers, the other is improved soundstage due to the ambience cues that were previously hidden in very low frequencies. You can read more about minimonitors and subwoofers at my blog here (scroll down). Both articles are targeted at new audiophiles but the basics are sound, I believe.
As you will see there, I am a fan of small high-quality monitors and subwoofers instead of floorstanders at a similar price point.