I have only one plant in my DWC now, but if I tried to move my plant out of its resevoir lid-hole at this point, some of the roots nearest the net pot would be damaged by being compressed against the edges of the hole as I pulled it out. So be wary of that - but if you're moving them at 6", it is less likely to be a problem (fewer roots).

To prevent the roots of one plant from becoming entangled with the other plants' roots, just check on them daily, and, with fingers dampened with rez solution, gently tease apart any tangles.

I don't know if this would work, but if you have trouble this time, maybe you could rig a separator... 2 large sheets of plastic, each cut most of the way down the middle and fit together to form an X, and then drill a bazillion little holes in them to allow for rez flow. You'd need an airstone for each plant though, and roots could potentially grow into/thru the drilled holes...

Ah well. Just check 'em every day. *grin*