I own M/L CLS IIz's. I've not heard the Roc, but I'm very content with the synergistic mesh created with a Genesis 900/CLS IIz combination. The 900 is the fastest subwoofer I've heard, and owned. Given that you're faced with the objective I was, needing something to quick enough to keep up with panels, I'd recommend landing a 900. The savings would be SUBstantial enough to justify the purchase of the 900.
Enjoy!
Coltrane1
Enjoy!
Coltrane1