Someone emailed me, and asked what I would do in a "cost no object" front stage.
Basically, if I was prepared to take a car and chop holes in the dash, what would I do?
This kind of system isn't in my wheelhouse whatsoever; I'm kinda obsessive about NOT building systems that reduce the value of the car. That used to be my thing; in the 90s I took the wheels of my car and cut a hole in the wheelwell to mount my midbasses.
I don't do that anymore because it makes the car un-sell-able.
If you're into that kind of thing...
I think that I would replicate a prosound monitor and jam it into the firewall.
For instance, these are the speakers that I use in my den. They're Yamaha DXR 12s. These things are capable of something like 135dB. When I listen to them, I generally have them set at about 2-5% of their maximum volume. These things are beasts.
The setup is fairly straightforward; there's a Celestion compression driver loaded into a waveguide that's about 12" wide. The woofer is twelve inches in diameter.
It's going to be tricky to fit a twelve inch woofer up front, but there's lots of eight inch woofers that get hella loud. A B&C 8NDL51 can produce more than 120dB from a single unit.
I'm a big fan of unity horns, and unity horns would work nicely here, but there's only one unity horn for sale (mine) and mine won't do 120dB. That was intentional; I didn't want to create a horn that would take sales away from Danley Sound Labs. So my unity horn is nice, but it's nowhere near as loud as the Yamaha DXR12.
I think that Mic Wallace has a really nicely engineered car, and I'd make mine like his if I were willing to cut into the firewall. I wouldn't use Image Dynamics horns, I would use something like 18Sound. That's not a knock on ID horns, I simply prefer symmetrical waveguides.
Here's an 18Sound XT1464, as an example of a nice waveguide. I've been using 18Sound XT1086 as my "goto" waveguide for speaker measurement for ages.