Really its a matter of how high the peroxide content is in the developer. The higher the peroxide, the more damaging it is. Personally, if you are looking to go darker I would stick with a semi or demiperminant dye. That way the cuticle isn't blown opened as much and pigment is going in to the hairshaft, not pulling it out. The end result is your hair can actually feel healthier.
ETA: personally, I have never had a good experience with boxed dye kits. I suspect that the developers in them are always going to be strong because they aren't sure if the user is lightening or darkening. A higher volume developer IS needed if you want to lift, but if your going darker you are just doing yourself undue damage.
Also, a good rule of thumb to keep in mind: however many levels of lift you are trying to achieve is going to determine what volume developer you should choose. A 10 vol will lift you 1 level, 20 volume will lift 2, and so on. But if you want to darken, always choose 10 vol or 20 volume. The difference there is 10 vol is demi permanent, and 20 vol will yield a permanent result. Don't let this terminology disillusion you tho... ALL dye fades, but a 20 vol will get the pigment deeper into the hairshaft. The reason why is because the cuticle is blown open more. Hair damage IS essentially a hair with a blown open cuticle.