Welcome EJG, and sorry to hear about the loss of your Dad.
Yes, for a subwoofer feed you could take a pre-level feed from one of the DIN4 signal in/outs on the Hicap. The Hicap wasn’t designed to run long interconnects so when Naim offered their own pre-level sub lead it was “slugged” with a 100R resistor in the DIN plug. It came in either a 5m or 10m length. You could look for one of these, or else have a lead custom made somewhere.
However, a better solution is usually to take a high level reference signal from the speakers themselves (provided the subwoofer has a high level input - e.g. REL et al.). Do your Kans have binding posts?
Of course, Kans themselves have a certain something about the way they perform that may very well be lost by adding a subwoofer. Kans are all about speed, timing and rhythm and it’s easy to lose that with a subwoofer that’s not optimal. So, adding a sub here may not be the best move.