Not sure why you started a new thread on this ..but anyway.
The reference monitor is not designed or suitable for a secondary feed to external monitors.
It is used to have two looks at same frame eg a composite and a scope
or two looks at different frames eg unganged . This maybe for a CC and grading comparison.
It is not absolutely vital that it plays in real time for either of these instances.
You can step through, but not play in real time. It just was not designed to do that as shooternz points out.
It will also scrub through.
This is generally enough for the functions one would usually do with a reference monitor engaged. eg fx.