The JBL VS3215-9 mid horizontal dispersion falls to around 60 degrees above 1kHz, it's on axis sensitivity probably near equal to the HF horn driver. JBL specs the crossover points at 300-and 1.3kHz.
A 3" driver has about 4-5dB less output than a 4" as used in the stock VS3215-9 .
Since you have added more bottom end, reduced the bandwidth of the 10" mid, and are crossing the 3" lower than the 4", the "aggressive" sound of harmonic distortion could be bothersome at 30 volts- THD could be 50-100% at 10kHz at that level.
I have not yet heard the DCX464 or the DCX354, but based on the output potential of your system and how hard you drive the HF, and distortion tests of both drivers, I'd would suggest the DCX464 would be more "relaxed" sounding at those high levels.
That said, the sound of diffraction throats at high levels can arguably sound more "aggressive" than THD at high drive levels, so a driver upgrade alone may not be the cure.
