Not posible, Equallogic only works with active/passive configuration. When you expand with more Equallogic devices you active controllers will
double. This has nothing to do with the Dell Multipathing Extention Module for ESXi storage, but it is the limitation of the controllers on the storage.
But why do you want more NICS? Do you have a problem with throughput? I think that your IOPS with a PS6500 will be more of a problem in the
future. When that happens and you also want more TB you buy a extra PS6500 or a Equallogic with SAS or SSD disks for more IOPS. Your throughput wil grow with a extra PS unit.