Water based for the poly urethane is a must anything else could potentially dissolve the foam.
I have the same Detrum 70mm combos and tried both 4S and 5S, but 6S sounds crazy
I've put these fans on a watt meter and it will draw 33amps and 54amps on 4S and 5S, respectively. So I'm guessing it will be well beyond the ESCs rated amps once you go to 6S. Also people on this forum who are using this combo on 5S suggest that before you do that that you balance the fans, which I have...just to be sure.