I have not heard them side by side. I did hear a full Klipsch THX system a few years back with 650’s for LCR, the 525’s for surrounds and 2 of the matching 12″ subs. The sound was excellent and the LCR’s were neutral ( they could easily be used as a studio monitor )
Having heard both the Classis series and Reference series in the past, my initial reaction was ” these can’t really be Klipsch”; they are that different from the rest of their family.
The Cinema 6 is neutral and should match up well, in my opinion. I think they are a bit directional for surrounds unless you can get some distance away from them.