Low-pass setting

the tools are not very expensive….. but not nearly as sexy as a new fuse or magic stone…

In my main setup I use a Velodyne SMS-1 bass manager that uses a microphone to provides acoustic room correction for a pair of HGS-15s.  I suppose it might be possible to use a SMS-1 with a KEF KC62.

6db is what you want to use as the 3db point will give you a hump at the crossover point. If you can highpass (cut the highs to the mains) then 80hz would probably sound better as the “bass” drivers in the Kefs are tiny and will need to travel pretty far to make a lot of output). 
Keep in mind the 6db point is NOT where the specs are but where they measure 6db down in YOUR room. 
60hz is a good safe starting point for most small speakers. 

I've observed the in-room response of my KEF Reference 1s using the SMS-1 display, and it comports closely with the KEF specs.  There is a gradual roll-off just above then a sharp drop-off just below 30 Hz.  That leads me to expect KEF's specs for average in-room response for the LS50 may be pretty representative.