I have no ideas for you, but don't want you to feel ignored until someone chimes in with one - but with what you are asking it could take awhile.

Most of us who are serious about getting the best sound out of a spider bridge reso with a pickup opt for the Fishman Nashville with a device to shape the sound like the Jerry Douglas Aura pedal. I think lap style players might be more picky than roundneck players who are playing a biscuit bridge guitar to get the most accurate sound. But this setup is expensive.

We also wouldn't typically play out Nashville equipped reso through something like an Orange electric guitar amp.

You don't want a surface mounted pickup like Krivo, which is my second choice after the Nashville setup. 

I will be interested to see if anyone chimes in with a hot plate-like idea for spider bridge reso.

I'm using the Orange amp primarily because I can make it growl a bit when I run up the neck on bottom round wound strings or hit single notes. which my ear likes to hear. I'll check into the Nashville further, initially passed over it for a simpler set up on the body like the hot plate. I can run the volume-tone pots with my little finger. Thanks for commentary-much apperciated.

Maybe l blinked in my reading comprehension . Are you running a generic under saddle piezo straight into the amp ? That has a tendency to sound unbelievably bad .

Since you mentioned the electric guitar amp , assocated with certain genres of electric music , and you are seeking * growl * , presumably you are after blues / rock / blues rock kind of sound , rather that faithful reprosuction of unplugged , that happens to go through a PA .

To give a better chance to what you have first , try ( something ) inbetween . Do you already have a basic preamp / DI intended for vertical accoustic guitar ? Or an EQ Pedal ?