That's an interesting question which I can't answer easily.
"Width" in MIR Pro relates solely to the perceived stereo information coming from the readily postioned signal source on a MIR Venue's stage, without the IRs - they get mixed in at a later stage. In that sense (and in quite a few others, too) the way MIR "thinks" is quite different from Dolby ATMOS. The latter allows for movable individual sources which isn't possible in MIR due to the static nature of the impulse responses the engine relies on. I would refrain from seperating the dry direct signal from the "wet" output, as any positional information you would achieve from MIR Pro would be lost instantly. It doesn't make much sense to move the reverberated signal either - all spatial relation between this signal and the other "MIRed" instruments of the mix would be destroyed.
Personally I mixed a quite a few movie scores that ended up in an ATMOS mix, though. In one them I ran two passes of the orchestra through MIR, using Main Microphone setups from different heights (Pernegg Monastry). These two passes ended up in two ATMOS "beds", one for the bottom layer, one (wet only) for the top layer. Worked out beautifully! 😊 But mind you, I didn't create any "movable" items for ATMOS objects like that, just static beds, so this might not be the answer you were looking for.
... I already mentioned the news in another thread: VSL is working on a next-generation version of MIR Pro at the moment which will introduce full 3D audio implementation (amongst other goodies). 😊 That said I have to point out that this _won't_ bring us signal sources which can move accross the stage while playing, sorry to say so.
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Off-topic side note: There seems to be some strange pronounciation rule that makes US-Americans misspell my nick-name "Deitz" instead of "Dietz" regularily. ;-D .... I'll have to explore the reason why, one day.
/Dietz - Vienna Symphonic Library