Here's a little secret. Go shop for a used keyboard amp. They are 'full range' setups intentionally, which is what a properly mic'ed acoustic amp really needs.

Guitar amps that are marketed as acoustic guitar amps are really just full range response amp/speaker/cabinet combinations. In the past, they often put brown tolex on them and brown tweed grille cloth to make you think you were getting something specific to acoustic guitar, but in reality, they are just a small combo PA system, which is what a keyboard amp is as well.

There used to be a big price differential between keyboard amps and 'acoustic' guitar amps, with keyboard amps being usually 1/3 lower price for the same type of features. This isn't true so much any more.

The other way to get to this pretty cheaply is to buy a little 4 channel mixer - You have many choices these days, and buy a single powered 'main' speaker for a P.A. system. Boom, same result.

Either the keyboard amp route or this suggestion above will sound much better than monkeying around with trying to turn a midrange-focused guitar amp into a full-range 'acoustic' amplifier.