I think the kn6000 is a great board, but this is a biased opinion as I purchased it based on my prior success with a kn1000, and without comparison to other boards ... the hard drive was pricey, but the alpha sort/search capability is a great option ... I have seen where some owners of other boards complain about the cost of technics boards, but then lament the fact that their board doesn't have certain capabilities or features that the technics boards have...
I believe you can switch floppies in the kn6000 while a midi file is playing, (its been a while since I needed to do that) but you cannot do a search on the floppy during play ... I think you might be able to do that with some other boards (?) ...
I would think that a used kn6000 in good condition and at the same price as the other 2 boards, would be a good deal ...
t.