K, I am playing in the worship team at my church, and whenever I go i bring my Gt-8 and my MG50 (i bypass the preamp and just use it as a speaker/monitor). The problem is, the sound coming through the PA is harsh sounding, sort of gritty, like when you record guitar through the stock soundcard on your computer, and it has gross distortion on it.

We've tried going direct from the emulated line out on my amp, direct from the output of the gt-8, and also micing the amp, but we still can't get rid of the gritty sound. It frustrates me that the other people won't hear my guitar as nicely as i do. Are there any things I could try to make it sound better? Or is it just impossible to make it sound good? (i hope not...). Thanks
If micing sounds just as bad/gritty as direct out, chances are the problem is in 1 of 2 places.

1) Your tone is bad/gritty

2) Something is happening somewhere between the feed into the FOH and the sound coming from the speakers.

I'd address #1 first, as #2 is unlikely to be a reoccuring problem in a commerical system.

If 1 isn't the problem, check what else could be.

Is the cable good? Is the mic good? What input are you running into? Is this a direct feed to the main system, or is it a pre-insert subgroup with some other post FX going on that could be altering your tone? Is your signal too hot and clipping the preamps?

Could be numerous things.
You mean the kinda digital distortion you get when your recording it on the PC? Does it sound ok through the MG, but bad from the PA?

In that case, maybe the signal going to the PA is too high, causing the distortion.... or somewhere in the chain, the signal is causing something to clip where you don't want it too.
If you get ok sound at home chances are the problem lies within the PA system. It could be a bad amp or even speakers and cables on the building. How good is the PA and is it your portable setup or the one wired into the church?

If the church PA is the problem I suggest buying your own portable PA system. This will give more control most likley and you should not have any problems.

That gritty sound you describe with recording into a stock computer is called clipping most of the time. but recording isn't the subject here...
try going direct out from the gt8 and bypass the amp all together...also mess with the different outs on the gt8...when i owned my gt6...i use to put in on the LINE/PA setting within the gt6 and it got the job done.