Hello majing,
You are right, MIR Pro is actually designed to have all instruments of an arrangement coming together on one stage. Logic is not too capable as a host, that's why VSL developer's came up with a workaround to allow for more MIDI inputs per VE Pro instance (see VE Pro's Manual for details).
But a workaround is just that: A workaround. So it might be a practical solution to use more than one VE Pro instance as a platform for MIR Pro, too. As long as you're on the same computer, you can open as many instances of MIR Pro as you want.
Kind regards,
/Dietz - Vienna Symphonic Library