What aawcy stated is absolutely correct. Ported subwoofers naturally will be more flat all the way down to 20-30hz. Sealed subs cannot naturally do the low frequencies because the frequency response curve drops off very quickly. The sealed subs require extended EQ to boost the very low frequencies to be able to produce the low bass you need.
You did not indicate which model SVS subwoofer you had. They have cheap sealed subs all the way up to huge powered ported subs. Your new REL subwoofers are probably a significantly higher sound quality and will have much better definition for music purposes than the SVS, but if you had a larger ported SVS, you might just have to accept the fact that the REL subs are not going to "shake the walls" like a big SVS. For home theater, there is no substitute for the big SVS ability to push air.
You did not indicate which model SVS subwoofer you had. They have cheap sealed subs all the way up to huge powered ported subs. Your new REL subwoofers are probably a significantly higher sound quality and will have much better definition for music purposes than the SVS, but if you had a larger ported SVS, you might just have to accept the fact that the REL subs are not going to "shake the walls" like a big SVS. For home theater, there is no substitute for the big SVS ability to push air.