Jock,
I've found (and measured) the Ohms (I use S100s) to be very neutral. That's sometimes evident in the lower midrange/upper bass where some high-end designs are goosed a bit to sound richer or in the upper mids where extra energy gives some speakers more"jump". IMO, neither of those approaches is a cardinal sin if the speakers' overall balance is appropriate and the deviation isn't too extreme. Notwithstanding that wiggle room, the Ohms just don't meaningfully go there.
Further, the top end of my 100s rolls off less quickly than some competing designs. The 100s also lack full range bass extension (as do most speakers at that price point). The overall impression may be "thin" sounding to some, but I'd call it pretty close to dead neutral.
I don't know your Kefs, so I can't speculate as to the issue you've ID'd. I can only note that the Ohms are quite neutral in my room.
As to Mapman's comments, Ohms are relatively rare speakers of unusual design. Mapman probably has more experience with Ohm designs than the rest of the board members combined. In this corner, his comments are always appreciated.