I have not tried the Rain, so I will refrain from commenting on it. Strictly discussing classical music and the signature that would have the best synergy with this genre would be the RE0. It has a flatter response than any of the above mentioned earphones, neutral and detailed in a manner similar to the signature of your FA-003. I'd highly recommend the RE0 before any other of the above mentioned earphones, but I would also suggest the RE400, which has fantastic control, detail, and balance, with very accurate and neutral mids (has a slightly more emphasized bass, but still quite flat and should not deviate much from your FA-003). While either the both the RE0 and the RE400 would be a good match for the classical music genre, I, myself, would go for the RE400 because it's more available, accurate, and is protected by a warranty when purchased from an authorized seller (unlike the recently discontinued RE0). The SE215 has a warm, mid-focused signature with a profoundly impactful bass and a fair treble emphasis (highs don't extend nearly as well as the RE0 and RE400). The FXD80 has a v-shaped signature which has a powerful low end, recessed midrange, and extensive, emphasized treble range. I will reiterate that I found that the RE400 had the best overall detail and clarity out of all the above mentioned earphones and would be ideal for the classical music genre (plus, it has a similar signature to the FA-003), and stress that it's at least worth considering. By the way, if you happen to find an RE0 on the internet that can ship to the US, would you drop me a PM? I'm planning on buying another.