You have to try it. I have tried DarT with my Wilson Sophia II speakers and it was OK (but not great in the bass department). System 8 has a bit higher efficiency but also bit more demeanding impedance/phase curves.
One thing for shure - it will sound VERY different than your 700cx (which I have also tried).
One thing for shure - it will sound VERY different than your 700cx (which I have also tried).