I should add that the character presets are a huge resource in MIR, one of the best things about it. Especially considering how one can use a slightly different color for a 2nd player or group. An example is setting your second violins to "dark" in order to make the 1st sound out more. Or many other variations. Using the "bite" variations in basses helps to make rhythms much clearer. ALso, I have started to think that it should almost be normal practice to use "clean low ends" or "clean mids" for various instruments such as harp and cello. Those presets represent an expertly tweaked example of the basic thing I was talking about with deep bass notes that certain instruments produce (such as a cello section) not being present hardly at all in normal orchestral settings, due to many factors but mainly 1) number of players, 2) resonance of the instruments involved 3) characteristics of amplitude in the particular range the instrument plays.
Also, the contrast of these levels throughout different instrument groups has a huge effect. If you are recording a chamber group, you will hear a huge amount of bass from low strings. If you are recording an R. Strauss sized orchestra playing "Also Sprach Zarathustra" you will hear almost NO BASS from those same instruments. Because the recording is adjusting for the massive brass and percussion that almost obliterates the strings at times. These factors are crucial to bear in mind during both mixing and mastering with samples, because there is absolutely no adjustment made for these automatically, quite understandably because of the goal of any sample recording to absolutely suck dry any instrument in front of the microphones and capture every nuance.