kindms and I have both. Our ck1's are old and not matched well , so we don't use them often, although I would go with the frequency response info from darby to my ears the ck1's are better for diffuse OTS type situations. I'd use the ck61's in any of the same situations knowing it is bit flatter in the 2-7kHz range
.for clarity- between us, we have 1 pr ck1; 3 pair ck61 ULS;