I don't have MODX+ schematics but MODX (not plus) supplies 3.3V out MIDI.   Since the MIDI Solutions Event Processor (Plus and also Standard models) do not show they are "Multivoltage" - these will require 5V.  It would be good to confirm if MODX+ supplies 5V or not.   If not, then MIDI Solutions suggests using a power adapter inline such as MIDI Solution's Power Adapter.  See the FAQ page on MIDI Solution's website.

I would doubt the newer product would use 5V since MIDI 3.3V is a newer spec to adhere to and MIDI Solutions itself says they are working on creating multi-voltage versions of all of their products to adhere to the new spec.  From what I can say none of the event controllers have been updated.  You may, however, also want to contact MIDI Solutions directly to make sure this is true.