Do a search for a review of the Sapphire written by fellow Agon member, kthomas.
I bought Kirk's C4's when he upgraded to the Sapphire's and I managed to get a brief, 15 minute listen to them. The Sapphires where not broken in yet, but they sounded quite nice... very coherent, blending nicely across highs, mids and lows. I did not find them to be lacking in bass whatsoever. I would see no burning need for a subwoofer with the Sapphires.
I suspect the Sapphires to be more room friendly than the C4's, as I'm in the process of installing acoustic panels in my room to tame the robustness of my C4's.
The Sapphires are also a smaller, more elegant speaker than the C4's... apt to have a higher WAF. The finish is impeccable and suitable for a formal living room.