You might be able to catch some video from one of the samples in the STVS gallery. It looks like it's password protected now (and someone here may be able to give you that password, or you can contact them). Here's the link:
http://www.stvsweddings.com/
However, my experience is that even in a video it doesn't really sound the same (think of the difference between hearing something live and something recorded).
Many, many brides have wondered how the solo violinist sounds (me too). And somehow you just can't imagine it in your mind. All I can say is...DON'T WORRY!! The solo violin sounds just beautiful!
At my wedding I asked that Disney songs be played for the groom processional, the bridal processional, the recessional, and the cake/champagne "reception". My only disappointment was that there was so much going on I didn't get to spend time really listening to the music...when I did hear it though, I was amazed at how beautiful it sounded.
Now, if music is a huge deal to you, then you might consider upgrading to something different. But, my thoughts on that is that the ceremony is only about 20 minutes and most of that there is no music playing. Spending a whole lot of money for extra musicians for maybe 10 minutes seems frivolous. You might find that the extra money you would spend on that is better spent in photography extras or extra flowers or some other extras that will make the memories even more special.
That's probably more than you wanted to know...
