When you are using a MXI-2 interface your computer is the controller. The PCI-MXI-2 (master) and VXI-MXI-2 (slave) devices are just bus extenders and therefore have no firmware. They have a configuration EPROM which stores data, but this is not firmware and therefore has no version. Basically, there is no firmware to read.
I assume "no firmware" on master/slave devices is only in a MXI system.
Due to obsolescence we are using the VXI-MXI-2 in its slot-0-controller function (not actually for MXI), I assume there's got to be firmware, and that your "configuration EPROM stores data, but this is not firmware" note applies only to MXI bus functions?