Hi there.

The rhythm guitarist in our band has this Digitech GNX 3000 multi effects.
He's new to effects and hasn't got a clue about tone or sounding good..
A thing I really don't understand, because that's a really important factor for me and especially when playing live!

He want to use it for effects only, no amps or cabs.. I've tried to figure out how to turn off the amps and cabs sims in the GNX 3000 but I can't make it work..
Can anyone help me with this?
I wanna help him out and make his sound a little better..

Unplug it? I had the GNX4 for bout a week, the RP355 for bout a month. The RP was a bit less frustrating to use but imo they both sounded like ass and aren't worth the money. I don't mean to be crass, perhaps its just me and my ears. I'm sure Fly will stop in eventually and give you some pointers, maybe he knows how to get a good sound out of it.

If you're in the US and have a healthy local Craigslist market, I'd bet he could trade it for a Line 6 M5 (maybe) or maybe a few individual pedals to get him going. Again, its just me and my opinion, but I wouldn't bother using that (or any mfx in a serious band setting).

Good luck!
Fender Mustang/Derfenstein DST> Boss Power Wah> Pedal Monsters Klone> Bogner Uberschall> Walrus Audio Janus> Randall RM20> Line 6 M9> Randall RM20
Select the GenEx row on the matrix, then select amp model "Direct". That will turn off amp modeling. Same with cab modeling, select "Direct". That turns cab off. The GNX series don't compare with modern multifx when it comes to amp modeling. It's a shame because otherwise they are packed with features. But since your friend isn't using modeling it should be fine.