Don't bother with VST software equalizers, get some hardware equalizer, I bet almost any hardware EQ will do better than the software EQs. I've tried lots of VST EQs (even very expensive ones $500) and neither of them came close to the built-in 10-band hardware EQ in the kX Audio drivers which are free.
I wish I would be able to tweak a graph rather than be limited to 10-bands but yea despite that limitation I have always been able to get far significantly better results on it.
I've been able to get all my headphones sound VERY similar on the hardware EQ I use, that's a good indication of how well they can work like when frequencies aren't (audibly) distorted no matter how you tweak them and you tweak the headphones with very different frequency response balance to sound according your personal ideal frequency response curve or at least get them very similarly balanced, can't change the soundstage etc ofc.
I've been enjoying buying lowcost basshead headphones and EQ the hell outta them as most of the time I find the cheap say 50~$150 headphones to either lack in treble extension or otherwise poorly balanced/muffled sounding which can be fixed very nicely with the hardware EQ. It's like overclocking computers like say buying a $100 CPU and make it perform like a $200 one.
Very few here seems to have experience with good EQs unfortunately. Often you pay $100 more for something you could almost fix with a good EQ.