One more thought... You might consider comparing different orchestrations of the same piece. For instance, Vaughan Williams' "Dona Nobis Pacem" was written for SATB choir, solos, and orchestra, but because the budget is always an issue, and many small choirs can't project over that much orchestra, he also wrote a reduction of the piece for small choirs using just strings and piano that is frequently performed. Take a look at some reductions of this type and compare how the composer resolves balance issues for the exact same musical material using different numbers and combinations of instruments. Could be an informative study! Youtube can be a handy tool for this sort of thing, since many people post videos with the score rolling by in real time for classical music. (Maybe not the "Dona Nobis Pacem," though. I'm pretty sure that's still under copyright most places in the world.) If you can't get scores that way, you can probably get them through inter-library loan. Librarians LOVE that sort of assignment!