Hey Scott,
The fret level/crown work is good as you not only get a better player, but it rules out that variable. Your ES2 is, indeed, the earliest of the preamps. And since you've already called them and they gave you the price of the current preamp, they clearly aren't going to do it for you gratis ...something they do for the original owner under warranty.
So my suggestion is buy a .050" allen wrench (I bought my set from Amazon for a few bucks), and adjust the three heads yourself. It's
not a drastic tonal or balance difference, but it does help a bit. I personally found the harsh brightness is due to the screws being too tight, which apparently the piezo responds with a sharp, brittle top end.
May I suggest: plug in the guitar and put ES knobs to detent. Turn up the volume on your amp (but I found good headphones through an audio interface to be more sensitive/accurate), and back off each screw until it is clear it
no longer has any influence on the volume. Then slowly tighten the screw sloooowly until you hear it affect the volume. HERE is where you tweak it "just so" ...and we are talking about
minute changes in the screw head to adjust the volume for that pair of strings. Repeat for the other two screws/pair of strings.
Shortcoming: that one screw affects the pair of strings unequally. For example, adjusting for relative volume for the high e will result in a B that's too loud; get the B where I want it and the e is not loud enough. Same with the low E and A. Ugh! I have no great love for the ES2, but adjusting the screws and lots of judicious EQ-ing (GEQ or parametric) makes it ok, passable; better than normal piezo UST (which I typically dislike), so at least it's a decent live tone once I've done all the aforementioned tweaking.
Sorry if this is too much info, or is simply irrelevant to you, but thought I'd just toss it out there as perhaps you find something of help.

Edward