implementation of a large number of outputs (1024+)
One approach is to use 32 or 64 channel LED driver ICs to drive the EN pins of the SuperTex HV816. 

AMS seems to be the key source for drivers beyond 48 channels, running all the way up to 144 channels. For instance, consider the AS1118, a 64-channel LED driver. Use the output channels to drive the enable pins, and you can control the individual EL panels that way.

While these devices are designed for driving LEDs, the 1.5+ Volt enable logic level of the HV816 permits an unconventional use of these devices, if a simplistic solution is desired: 


Simply configure the LED driver to its smallest current level, use that to drive any red LED (1.7 to 2.1 Volts typical), with the EN line of the HV816 wired across this LED. 
Each LED lighting up will not only enable the corresponding EL driver, but will give a visual indication of operation, as well.


This is assuming that the design has separate HV816 drivers for each EL panel. If not, please share the schematic for how you have the matrix configured, for further suggestions.