I'm pretty at making just about any sound I want with a synthesizer, that is, in its shape and timbre.

But the sound itself always ends up sounding sort of brittle and weak, even harsh.

For example, Zomboy/Skrilex have very loud and distorted bass sounds, but relatively speaking, they have this really nice sort of creamy/fuzzy sound to them. They're not all metallic and harsh.

Basically, I make the midrange sound, highpass between 100-200hz depending on the sound, and then from there I don't know what to do at all, never have. Sometime a lowpass really high between 18k-20k, but that doesn't make a huge difference. Everytime I try to go a bit deeper on EQing these sounds I end up doing more harm than good.

In terms of volume in the mix, I don't think thats the issue. Everyone mixes differently, but in this style most of the main elements, like kick/snare/mids/sub, the volume of each is pretty similar track to track.
 
Any tips?

I don't use multi band stuff, but from what i've read about it and with experimentation and eq should work just fine.

You might need to get a low pass and a high pass as well.

Consider how you want to build your sound and what you want to focus on.

and by what you described you might need to introduce different distortion types and settings on each layer you have.