Sorry - this thread somehow slipped from my attention ... 8-)
Knievel, most of the approaches I would have suggested have already been mentioned, but I'll try to give you my point of view nonetheless.
First of all: It is true that the a convincing mix always starts with convincing sources, which are composition, arrangement, and performance. The performance is even more crucial when it comes to virtual orchestration, but a good arrangement can make or break a mix. Of course it is possible to "fix it in the mix" (... I have done this more often than I would admit), but I always try to get rid of all instruments that compete with each other for space - both frequency-wise as dynamically.
Second: Give your instruments the proper space! Vienna MIR is all about space, so don't stick to traditional concepts, and don't try to stick to a seemingly "convincing" visual setup. Use you ears. Try different positions for instruments, rotate them, and trust your instincts. And talking about space: Don't forget that a different main microphone position will change the acoustic properties in a way that it sometimes seems to be a different room. - Actually I would suggest to try different venues, too, but you obviously you can't do this as you are still using the demo version. The Mozart Hall of the Vienna Konzerthaus is maybe the world's most famous venue for chamber music, but it wouldn't be my first choice for a huge modern composition with lots of percussion, for example.
Talking about the main microphone: You know that you can change the setup of the main microphone at any time, don't you? There are quite a few presets available in the pull-down at the top of the Output Channel, and again each of them will sound different. The Bumlein-array of two crossed figure-eight microphones will give the room more width and brilliance, for example (which might help in you case, but could be perceived in a "lack of warmth" in another context). - Of course, you can also create new main microphone setups in the Output Format Editor.
Another aspect of the main microphone is its volume opposed to the dry signals from the instrument themselves. You may either change the ratio on each instrument individually, but it is always a good idea to fine-tune the ratio globally in the Output Channel (... don't forget to press the "Dry Solo" button from time to time, just to remember what it sounds like _without_ MIR ;-) ....).
There is a "Wet Solo"-button, too. Use it to spot any irritating resonances (or "muddiness") in the room signal, and use the dedicated Room EQ to get rid of it. Be aware, though that there is not one solution for all times - it might very well be that the problematic aspects are very different in another piece, in another key, with another arrangement and stage setup.
If you are feeling better with the changes up to now, you can also try the so-called "Character Presets" for individual instruments. They give you the fast, but tailor-made possibility to _individually_ change the sound of an instrument or ensemble. More ore less all Vienna Instruments are covered here with settings like "Air", "Bite", "Warm" or "Distant".
Further down the line, you will need an EQ for certain instruments, to tame some over-boarding bass frequencies or resonances (this is a problem with any recording, not just when you deal with virtual orchestration and MIR). Also, giving the source some "grip" on behalf of gentle compression can do wonders - also in classical music (.. don't trust all those urban legends that compression is bad). You could either use Vienna Suite plug-ins, or your favorite VST processors. - A very new approach are the Tilt Filters in the SERTI/FORTI-collections for the Vienna Convolution Reverb, BTW; they don't reverberate, but change the frequency distribution of an instrument in a very unique, but musical way.
In the end, you could do some final touches with MIR's Output EQ. This is for overall adjustments your mix might need. As the EQ is our mastering-grade, high-quality algorithm, you could try to add some treble with a smooth shelving filter (+2 dB at 16 kHz with a very low Q is always a good starting point.
... I hope this gives you some ideas for your MIR demo tests. Let us know how you proceed!
Kind regards,
