I've owned CM6 S2's for about two years now. Today I went to listen to the new 700's. Only the 705 S2 and 702 S2 were available to try out. No CM models out to compare.
I'm far from a speaker reviewer, but here are some brief notes.
The 705's sound great to me and similar to my memory of my CM6's. Compared to the 702's, I liked the overall sound of the 705's a bit better. Obviously the 702's had much fuller sound down low, but it wasn't for me.
705's compared to some 685 S2's - massive difference. Tweeters in the CM and 700 S2 series sound so much better to me.
Fully aware that I might get home and not be able to tell the difference compared to my CM6's, I went ahead and picked up the 705 S2's.
Back home, I set up a super scientific comparison with a CM6 S2 on the left channel and 705 S2 on the right. I use a Peachtree Nova300 for amplification. I've never been sure if break-in is really an issue, but these were fresh out of the box.
The result: There definitely noticeable differences.
I thought CM6's had a deeper bass response. It sounded a touch boomy compared to the 705's, but always sounded fine to me in the past. The high's sounded clearer and a little more balanced on the 705's. Overall, I mildly prefer the 705's sound but it's fairly subtle. Or, my expectations for the latest and greatest are just reinforcing my perception.
Conclusion, if you're interested in upgrading from CM's to 700's, I think there's a noticeable difference in how they sound. It's certainly worth a side by side listen, if you have the opportunity. You might end up liking the CM's better. Unlikely to be a life-changing upgrade. I like the silver colored drivers better.