The KC62’s owner manual doesn’t address the issue of high level connection to amps that don’t ground at the negative speaker terminal. Their website’s instruction page https://uk.kef.com/blogs/news/simple-subwoofer-connection-tips doesn’t address the connection issues to differentially balanced amps either. With REL subs, you just don’t connect the wire that usually goes to ground and only connect the two positive terminal connecting wires. You would need to contact KEF directly to see if that would work or if you must use one of the other three methods with balanced amps.