OK... thanks for not taking my comments as a flame.
I have to run out now and I will contribute at length tomorrow -- but in short, the default settings of a mixer should never be "0" (which is really -0dbfs) because there would be zero headroom for your mix. it all has to add up (the sum of the parts). You need some headroom.
Numeric settings on a mixer are meaningless -- what if the piece is ONLY a solo violin? The overall level of the instrument will be proportionally greater. Much greater. What if the solo violin is simply representing 1st chair, and you also have 40 other violins also playing along?
Now here is where the MIR philosophy will contradict basic techniques -- since for realism (MIR's strength) there are basic truths to acoustics and where and how an instrument will live in an acoustic space. BUT we're making RECORDINGS approximating what we think we hear in these spaces, be it the Vienna Konzerthaus or the Todd AO scoring stage. So your levels are truly arbitrary. WHAT IF the soloist plays 3 times louder than the ensemble, because he's an egomaniacal jerk, and the conductor can't solve this? What if the soloist is paying for the recording session and wants his mic louder, irrespective of the "proper" balance.
I have only demo'd MIR, and am waiting for the rumored "pro" version, which is rumored to integrate VE Pro with MIR before I move to use it, HOWEVER, it is my understanding from listening to the creators, that MIR is designed (at its most basic use) for truth in placing samples into a space, and the integration of the instruments into the space.
So you have to start somewhere. So if they set the default to -22 (in gooney units, arbitrary), then that's where it starts, but that does't mean anything. Move the fader to where you like it. but pay attention to gain staging.
I have to run now, and I look forward to answering your mixing questions tomorrow and beyond. Remember to always trust your ears.