John ... I am using the Z-5500s for my kn6000 and vocals ... I (and the customers) love the sound ... I have not yet tried the sub with other sats (perhaps I'll give that a try this weekend) ...
In all my years of playing gigs, even with the band, I had never used a sub ... I really like the difference it makes ...
I only wish the kn6 had separate outs for the bass and drums as does the kn7 ...
Doug is right in that you really have to try different subs with YOUR gear ...
good luck,
t.