With an acoustic guitar, is it appropriate (i.e is the sound quality retained) to run the guitar through a high end electric guitar amp? I'm considering buying an Orange Crush 120C amplifier for my electric to play gigs with, but I also play my acoustic live a lot. I don't want to sell my amp that I use with my acoustic (Marshall 50DFX) if the sound quality through the Orange for an acoustic isn't as good, however the money would be useful towards the new amp.
Electric guitar amps are not intended to faithfully reproduce the sound of the electric guitar, but to shape it and give it a new sound entirely. Alot of people will buy their electric guitar amp on the basis that they feel it gives them the sound they're looking for.
As for amplifying acoustic guitar, that's not quite the case because the whole thing about acoustic instruments is that they have their own acoustical properties and we're trying to take that sound and make it bigger for a larger group of people. But we don't want to wreck it. There may be a bit of artificial reverb, or some subtle EQ and tone-shaping.
So, yes, you can buy a dedicated acoustic guitar amp, but have you tried playing your acoustic guitar through a PA, either miked, direct, or some combination of those two? If you want good sound, you should apply some signal processing and then reproduce the sound faithfully through either an acoustic amp or PA. And the transducer source (pickup) may be one of the most important things in this signal chain. In my experience the best results are from blending a good pickup with a mic.
There are in fact acoustic guitar amps out there that you can buy for this purpose. If you have the money to spend on it, I would definitely recommend that. Other than that, regular amps are okay for acoustic guitar, although you'll find that the sound is not ideal this way. Additionally, acoustic guitar amps use notch filters to prevent feedback, which is also something your regular amp would be lacking.
Yes, it's okay, no big difference.
Actually, you only need pre-amp, equalizer, and a reverb. But, if you're playing in a big gig show, soundhole cover is needed to avoid the feedback, but in some case that your acoustic guitar already have notch filter or feedback reducer, it's fine not to attach soundhole cover. I always play my acoustic through electric guitar amp (Marshall MG30CFX), with crunch mode, sounds good, and it's okay.