Careful there, the reverbs in the VS do not do the same thing as MIRx. MIRx doesn't combine aspects of MIR and VS - it's the little brother of MIR. The Vienna Suite convolution and hybrid reverbs are different kind of tools.
They are reverb plug-ins in a traditional sense. You set up a reverb and send your audio/VST outputs through. MIR/MIRx is a "multi impulse response" software. They don't send all the instruments through one reverb - every instrument gets its own convolver with their own impulse responses, and has its individual "spatial representation" in the virtual room that's being simulated.
Technically, MIRx does the same thing as MIR (and sounds the same), but without giving access to all those parameters and in-depth functions MIR comes with. So, MIRx is the easy-to-use, stripped-down plug-and-play version of MIR.
An experienced engineer could use the VS reverbs and power pan to create comparable results - for example, by setting up multiple instances of convolution reverb for the ERs of different instrument sections, and creating the reverb tail with the algorithmic reverb. But unless you really know your stuff, I would say that MIRx will most probably do a better job putting the VSL instruments in a plausible sounding space that one could by traditional means.
MIRx is intended to be used on its own, it doesn't rely on any additional panning or reverberation. You can of course experiment with reverb plugins in addition MIR/MIRx. It can work fo tails - if you pull the MIRx dry/wet slider all the way to "dry", you sort of keep the spatial positioning of the instrument, but eliminate the reverb tail of the venue. You could then create the tail with a reverb plugin and send the VST outputs through that. It can actually sound pretty good. But it's more something that you can potentially get away with, so to speak - not something you should be doing. As said, MIRx is intended to do the job on its own without you having to set up additional reverbs or panning things around manually.
