Just like what Boogified mentioned, it's usually the shitty amps... the amps are oftentimes peavey, crate,
roland jazz chorus QUOTE]
WHAT?! the roland jazz chorus is a great amp, better than crate and peavey. it does not deserve to be rated in the family of crates and peaveys. this is of course my opinion
Yes, I agree with you to a certain degree but you have to spend some time with them to have a decent tone specially on gain-y tones. If it's your first time to encounter one, you may find it very difficult to get a good balance between clean and dirty tones.
To the OP, should you encounter this amp, one thing that works for it though is to keep the bass low, maybe just on 2(I"m using a strat so you may have to go on 0 on a Les Paul), and keep the mids and treble at around 5 to make it sound flat. Then just use your pedal's EQ and gain to add flavor to it.
Problem is, the ones they usually provide has some crackling pots or just one channel working. Not that you'll need two but it can be a disaster if you were plugged into a faulty channel unknowingly and you're troubleshooting your whole rig with just 5mins to balance your sound with the whole band, stuff like that.