Proportion Between Volume of Different Instruments

Hello,
Admitfully, I have never heard an actual orchestra play in my short life, so I wouldn't know what instruments are most heard during the playback. But, what I do know, is that the Trombone is quite loud at Musescore's playback. Then when I export it as a midi file and play it in VLC, it can't be heard. The trumpet is noticeable in VLC but also has the same type of problem. The clarinet sounds the same on both Musescore and VLC, but it still concerns me, since when I look at other compositions that have two clarinets, they don't seem to make such a large effect like they do here. Of course, if I use the mixer or add dynamics, then it affects the midi to be as well.
My question is, which playback am I suppose to believe that has a more real proportion between the volumes of different instruments?

At the same time, I'd like to say that I have tested Sibelius 7, and it looks less than good, not comfortable at all, and it sounds very bad (and I had expectations of those GBs of sound packs...), so I'm waiting (eagerly) for Mususcore 2.0.

Also, I watched the movie "Copying Beethoven" from 2006, it's cute, but bad in my opinion.

- HolyEyE