I play the violin as well (not as long as you have, but I get by), and the only headphone I've heard with proper timbre that I can use to monitor and record with the piano, violin, anything acoustic, would be the LCD-2. Obviously that's not an IEM, but it's really hard to find something that comes close. They don't mesh well with my current sig tastes, but I will keep them forever for that reason alone.
BAs might not have the timbre you're looking for, but it really depends on tuning in the end. The W4s are some of the best universals I've heard for classical, the timbres is among the closest as you'll get from BAs. The EX1000 do much, much better in this regard, and if you won't mind the fit and isolation, I think these will be your best bet. Get the ER4S first and see how that goes.