The problem I am having is I too have a zillion MIDIs that I have done with regular old string patches and now I want to break these up into sections. The problem is I know squat about classical orchestration. I understand theroy, but I get lost in what typically doubles what. When I take a stab at breaking things out, it always sounds way to thick (I double violin sections to play an octave apart and it sounds liek 50 violins. ) or way too thin (I assign a 4 or 5 part harmony with each line played violin 1 (or 2 for a darker timber), violin 2, viola, cello, bass. Now, just out of my ignorance, I don't know how else to appraoch this. There is a happy medium out there and I just don't know what I am doing. I know there are rules (or techiniques rather than rules) for cellos doubling basses an octave up and things like that, but I don't know where to start. My goal is to take these MIDIs I have done with old skool "Full String" patches and brek them out. Genre wise they are all neo-classical kind of stuff. (What my mom listens to to go to sleep to.... Andrea Bocelli, Josh Grobin, Sarah Brightman stuff... You know, movie string sounds in pop songs, what every newbie asks about.) Any suggestions from you fine folks?
For a general answer, get an orchestration book (Adler, Rimsky-Korsakov), preferably one that has a companion CD and study the examples while listening to them. There's no single magic combination of orchestration rules that work in all cases. Take the time to study scores and it'll pay off.
For a more specific answer, I'm looking at a Josh Groban score as I write this. For delicate passages, the strings are muted. In quiet sections with full harmony in a low register it's pretty much block chords. For instance a mp "C" chord is voiced, (top to bottom) VL 1 (E - 1st line) VL 2 (C), VLA (G), CELLI (div. E & G) & Basses on low C. Nothing exotic. Low strings are voiced a little wider apart than high strings.
In a section with a little more tension, the violins have a moving line played in octaves, the 1st violins not going too high, the low strings stay in block chords. At the end of the phrase, the violins switch from octaves to playing in 6ths.
When you hit your big key change (and all of these songs have them) the low strings are still in block chords, the viola might switch to divisi to add a slightly higher voice to the chordal accompaniment. The violins are usually playing a dramatic line in counterpoint to the vocal melody in unison if it's not too high, split into octaves when really high, then play in 6ths again at the end of the phrase.
Nothing that I wrote should be considered to be "written in stone". Study scores and listening is your best path.
I'm in the same shape you are in (although I only had a few midi files, not a zillion). One of my first realizations was the GPO intstruments were limited to their real ranges, and as you noted, most midi strings are all lumped together.
For the midi files I had, I just had to experiment and see what sounded best at first, then I tried to read and learn as much as I could to see how it should be done. I've still got a lot to learn. I don't think there's a short answer to our problem.
In most cases, even after breaking the midi string parts out, it just didn't sound the same. It's just that GPO is so real sounding, and the string patches I use have a certain quality about them, but it aint real. They fit nicely in certain type of songs-- where, ironically, "real" sounding strings sound kind of out of place.
I think the same goes for most basic generic orchestral sound patches.
So I've temporarily abandoned the string section patch midis and started playing around with writing tunes from scratch, or mocking up orchestral midis that have proper string parts. Or taking string section midis and breaking them out by listening to the actual recording--in the one I'm doing now, the midi was nowhere near the notes played by the strings on the actual recording.
This also develops your ear for picking out the different string parts.