OK, update. When charging 2 5000 6S together on the 615i Duo3 @27.2V in to the charger the 45C'c and VX's start out taking about 7.5A and end up about 7.1A
I haven't been able to get up to a 2C charge with my 615 Duo on the 5000 6S, the 180W/ channel just won't go above about 7.5A even with 27.2V into the charger.