Wayne,
The "DI" factor loses me. I know I just tried out my 1st JBL compression driver(2426J). I used the 4 Pi-pro figures(15 ohm shunt and 33 ohm series/.33 ufd cap). I also used .68 ufd bypass caps on the PE 1.6 khz hi-pass crossover. So far I think the caps are still new and not smoothed out(less than 2 hrs time on them). I find the JBL to be rather bright in the upper midrange/lower treble area used on the Martinelli horn. I know that the 2426J is a 16 ohm driver, but I have used Altec 8 ohm and 16 ohm drivers without changing up the crossover with little difference of sound.
I think the JBL with titanium diaphram is more brittle sounding than the aluminum of the Altec drivers I have used. I set up the crossover this time with easy "connect/disconnect" terminals to swap out the horns quickly.
I have my Altec 902B on my 650hz Edgar horn and will be trying it out tonight. I think the JBL needs less HF compensation than the Altec 1" drivers.
Ron