I use the K600's with my system (Linn AV 5103, 5x AV5105 and AV5140's front, AV5120 center) and love them. I haven't gone active yet, but certainly will after returning from Europe in May. I picked up a pair NEW for $140 shipped with super deltons on all 24 end, they where the best finished set I've seen in the K600's. So good I sold off the 2x16' ($175)lengths I was going to use. I think if you're going to go activ, it certainly simplifies the whole wiring situation (ie you don't have three seperat sets of wire to you're speakers). If you look around, you'll find some fairly cheap. Try here and Ebay (that's where I found mine)
As for upgrading the wires, I got mine terminated on all 24 ends, so they are tri-amped now. The AV 5140's have 4 sets of speaker connectors per channel, so going from one amp to three isn't an issue for me, I'm not sure of the number of connections on the Lk140, if it's three or more, just buy them fully terminated and you won't have to worry about upgrading. I have the amp ends cut apart for 16 inches, allowing me to spread out the amps on my rack.