David, here are two examples of solo violins from Kirk Hunter’s Diamond Orchestra:
https://dl.dropbox.com/u/97281321/romantic.mp3https://dl.dropbox.com/u/97281321/Strat.mp3The first is a solo romantic violin and the other is a solo stradivarius.
The only thing I did with your midi file was to extend some notes so they would play legato. They were choppy as they were however I know each sound source is different thus you have to program midi differently for each one.
I choose these two examples because they had built in vibrato. There are many articulations for each, including some no vibrato ones, but I thought that these sounded the best.
You will note that some of the samples stop abruptly. With work this can be eliminate but I wanted to do as little work on your original midi file so you could hear the sound difference only. You can get some very convincing string parts if you take the time and use up and down strokes, a different sound source for each string part etc.
Although this orchestra is a little on the expensive side but for me the bang for the buck well worth the extra money.
Let me know what you think.
edit - I should have pointed out that no effects were used on these sounds. They are straight out of the box sounds. With reverb and other effects these will more come to life.