You will not free up any power on the Rogue. To free up power you would need a separate amp and preamp and a sub with a high pass filter. If you use a sub you will be running the speakers full range!
Best course of action
I’m using a Rogue Audio Cronus Magnum 2 integrated amp paired with Vandersteen 2ce Signature speakers and I’m very happy with the sound, but of course I can’t leave well enough alone. I’m considering either adding another amp (solid state) to the low end to biamp the system or adding a good sub. I’ve been told that setting a sub for the bottom 80 hz will not only improve the bass dynamics, but will free up some of the Cronus power for all frequencies above. My musical preferences are jazz, acoustic and classical with some rock and roll, but no really high volume stuff. Opinions? (This system is not being used for home theater.)