This speaker is not designed to work with a sub woofer.
The 5 way Veritas 2.4 dual ported design is known for an impressive and weighty base. Energy do not state their THD figures but they do say that 25% THD is acceptable in a high-end speaker and that they do even better than that. I suspect that the ports are tuned somewhere in the 20 to 40 Hz range and account for the amazing bandwidth of these speakers.
This is an excellent design to get all that low end bandwidth, however, the tuned ports, which bring these amazing LF benefits, might bring some drawbacks when you add a very high-end dedicated sub woofer.
See this article on pros and cons of tuned ports;
http://www.soundonsound.com/sos/oct00/articles/monitor.htmThere is no doubt that the REL 12" woofer should do an extremely accurate job over the ultra low frequencies, after all, it is dedicated just to that task alone and nothing else.
IMHO, I suspect that the tuned ports on the Veritas 2.4 might be masking any audible benefits of a more detailed/accurate ultra low frequency output that you might get from the dedicated REL sub.
BTW I had some Energy Pro 22 speakers in the past - awesome speakers!