Easy, they are already in 6-pax. Those aren't propagation trays like you would use for impatiens and shit.
What I do is wait for them to get pretty rooty. Not quite rootbound, but just to the point where they are starting to show very slight N def from having used up ALL the existing nutes in the starter mix (~40% perlite, 50% composted manure and humus, and 10% worm poop).
Then I let them get pretty dry and poke the bottom of each cell in the 6-pack until the soil plug frees itself from the sides. They just slide right on out. I think there's a transplanting pic or 2 back earlier in the log.