fuzztone is exactly right.
Ported or sealed no amount of room optimization, correction or equalization will ameliorate the sound stage optimized null location of your speakers and allow the ability of -3dB subwoofers their full potential for room and system integration and performance.
Your REL isn't nearly as restricted by room positioning often placed next to speakers. Since their lowest frequencies are down -6dB sub-bass speakers simply do not excite a rooms modes like subwoofers, at the expense of extra low frequency detail and heft.
Save your money and just use the REL.
In the mean time try and organize an in home comparison audition of dealer positioned Vandersteen Trio's. With your family present you'll easily hear Paradigm's coherence paradigm. For me this became a far greater priority after living with three of the Canadian's top models.