You've got too many variables, firstly with the amplification for the JBL. I found the 435Be to be rather ordinary if I'm honest.   The 1500AL however is capable of supreme sublety IME - the ATC is more punchy. The JBL is really a mini monitor being -6db at 45hz, the ATC more full range. JBL's equivalent of say a 150 would really be a 4348 or historically, a 4344 or 4345. Those are studio monitors. The speakers you compare are very different beasts designed with different goals.