Sound quality of the unit itself is very good. But, depending on what you are running it through, it could vary. I have used this unit with a couple of different setups. I use 2 Fender Strats, one is a stock Deluxe Super Strat, and the other is/was a Lone Star Strat that I modified with new pickups in a H/S/H config. When I first got the AX1000G I was running it through a Fender Hot Rod Deluxe, then miked through the PA. This setup sounded best without using the amp sims. I don't think there is really any way to make a 1-12 tube amp like what the sims are supposed to be. It's just to colorful. Now I am running it direct thru an eq to it's own PA. QSC 1400 watt power amp, 2 Yorkville SP210 subwoofers and 2 Yorkville tops in stereo. This is my onstage setup. I could just go direct into the mixer, but I wanted some sound on stage to resonate my guitar for harmonics and monitoring purposes. The amp sims really come into their own through the clean power. The acoustic simulator never really worked very well through the Fender, but sounds pretty authentic through the PA. It also seems to sound better witht a single coil pickup. I can now dial in pretty much any sound I hear on my cd collection. From a jangly SRV kind of sound to a really heavy KoRnish, to tubey classic sounds. The clean sounds of the sims are nice also. I tend to use the blackface 212 most though. Chouruses are allright, I don't lay on effects to thick usually, except for the Pink Floyd patches that I made. The delays are great. The autowah is nice, but I don't use the Vox wah. I don't have any use for some of the uncommon effects like the pitch shifter and ring modulator.
It's pretty dependable, I have had it for about 4 years now and the only real thing wrong is the #3 button is starting to get a little intermittent. Maybe one of my kids spilled something in it? Also once at practice, I got some good country radio through it on my high gain patch :-). I wouldn't gig without a backup, but I have a backup for everything just in case.
I have been playing in the same variety band for about 6 years now with varying setups. http://abe.midco.net/vitalsignz
This is a very nice tool for my type of play. I'm not a real "tone-freak" like some musicians are. If it's close, it's ok. The drunks I play for 99% of the time don't care if it's authentic or not. I've used rack gear and a maze of floor pedals before, but I am coming back to the Korg. For a long time I was just using it at home with the headphones (which sounds incredible by the way). If it were stolen or lost, I'd probably get the 1500 because this one is about 4 years old now anyway. I love the tones through my "PA" style setup. I don't really like it through a regular guitar amp. I think I like the acoustic sim the best...or maybe US high gain in the 4x12 modern...ugh, must be a tie. I didn't really compare it with other stuff, but I did mess with it for a few hours at the local shop before I bought. I wish it had more storage rather than factory presets. The delay between patches isn't a very big deal once you get used to it. I really like this product. It has drasticly reduced my setup time and eliminated a lot of troubleshooting. If any of you have a large pedal setup, you know what I mean!