As a compromise between using an \"ensemble\" sound (which sometimes sounds synthy and unconvincing) and using several individual solo instruments, I have discovered that combining an ensemble with 2 or 3 solo instruments can often yield convincing results - with the added advantage of not consuming too many instances, system resources, or polyphony.
Here is a very short example I threw together in a few minutes, using only 2 instances of GPO. In instance one, the first 4 slots are set (respectively) to 3 individual violins and a violin ensemble patch (thus making up the first violin section), all on MIDI channel 1, and the other 4 slots are set to 3 different individual violins and a different violin ensemble (making up the second violin section), all on MIDI channel 2.
In instance two, the first 4 slots are set to 3 individual violas and a viola ensemble (on MIDI channel 3), and the other 4 are set to 3 individual cellos and a cello ensemble (on MIDI channel 4).
Hence, an entire and (somewhat) convincing string orchestra using only 2 GPO instances and 4 MIDI channels:
Please let me know what you think.