MIR is not a VST like VE so you can't see it in your active devices.
You have to link SIB5 and MIR via virtual midicable. I use LoopBe30. Once you install the virtual midicable this does show up in your active deivces as "Internal midi" 1, 2 3 etc to 30. LoopBe30 gives you 30 virtual cables (or ports) and each cable(port) has 16 midi channels (so theoretically 480 possible channels - that would be quite an orchestra!)
So you set up your SIB playback configuration with as many midi channels as you need (16 per internal midi device) and set up your mixer so that each stave corresponds with each midi channel then you set up MIR so it accepts midi from your internal midi devices/cables and set each VI to recieve midi from the corresponding SIB stave and all should be well.
Fiddly but it works. If you do go this route more details for each step can be given.