A higher quality setup (DAC/Amp) will add refinement to the sound, but won't change the sound signature of your headphone.
I would say try to pick the headphone that suits your preferences the best. Then improve your setup around it.
If you feel HE400i gives you what you like (in terms of bass quality and quantity, midrange and treble presentation, soundstage, fit/comfort and finnish, etc.) then sure, there's no need to get a different headphone. Get a better setup and what you already like will get even better. But if you, on the other hand, don't feel the HE400i is the one for you, for one reason or the other, then check those different headphones. Each of them will present sound in a different way and you'll surely enjoy some of them more than the others.