Hello Bogdan,
thanks a lot for your interest in Vienna MIR!
From MIR's point-of-view it doesn't make any difference how the MIDI data that control the instruments on its stages is created. It could be a MIDI-sequencer (on the same machine or on a second computer), it could be a pure notation program, or even notes you play live on a MIDI-keyboard.
In that sense, any piece created with MIR could also be something that could be a demo for Sibelius & MIR, too. :-)
Kind regards,
/Dietz - Vienna Symphonic Library