Well, 80dB isn't quite low either. My favorite local jazz club's PA is leveled at a max of 80dB, and I have to agree that the FX700 are too V-shaped for that sound level.
But if you wear them with a loose seal and listen at lower volume, they're one of the most amazing IEMs for classical, their timbre being only equaled by the Sony EX1000 and Widing ME-10EX imo.
I have the XBA-3 too and no doubt, these are better allrounders than the FX700. But for classical at low to medium volume, I'd pick the JVCs over them 9 times out of 10.