Just FYI, its only one violin. I believe I know what part you are talking about. I did succeed in losing my lone recording, and my copy of the score. I've worked on this mvmt many, many years ago, so Im decently familiar with it. Its just one violin. Yes, this mvmt is very difficult, and unlike a lot of other violin works, this one is ridiculously demanding in terms of right arm endurance. And the contrapuntal lines are not described as "out of tune", for they are perfectly in tune.
Once you get over your shock that a single instrument can do that, you should check out Bach fugues. If you love violin, try the sonatas and partitas. My favorite Bach stuff are fugues for the keyboard, if I had to pick something.
edit: recommendation
http://www.amazon.com/Bach-Sonatas-Partitas-Solo-Violin/dp/B000001GXY
though the Perlman recording will have better AQ most likely.
edit #2, though I like Milstein, I don't recommend his Bach as much, just throwing out my opinion...