hi garacco!
i would just say....give it a try

the nyx jumbo pencils are really cheap, so for experimenting they would be cool.
i dont know why the dark pencils make some colors pop. hmmm how can i explain...
i personally use shadesticks nearly every day. they work fine for me as a base, and they make colours "pop". so they have 2 points.
when i would use a colourless / neutral base it wouldnt pop the colours so much. thats why i rarely use updd or other bases. (actually only when i pull on matte looks i dont use shadesticks)
i dont have jumbo pencils, so i dont know if they are shimmery or matte, but i think most of them are shimmery.
so, to explain....the shadestick can change a colour. for example when i apply a plummy brown eyeshadow over a purple base than the plum is more in visible.
when i use a brown stick under it, the brown pops more.
thats also interesting when it comes to duochrome colors, for example the "label whore" from too faced, which is dupe for mac bluebrown pigment.
i like the blue side of this colour more

so i use a blue shadestick under it. it helps to pop the blue in it.
then i have some very light shadesticks, like mac overcast. this colour i use for every little *****y shadow, that is too light in my oppinion, too sheer. some nyx shadows are kind of too sheer for me. with a shadestick they get more bold then with a base like udpp.
even you can make total different effects. use a yellow shadestick under a blue shadow, and the result will be more green. and so on and so on
SOOOORRY for this long text but i have some problems with saying what i really want to say in english =/
if you are interested in a few example that u can SEE! then i could do some swatches tommorow. perhaps you would like, then just say it

now i will go to bed, byebye
