In my opinion, the ifi DACs are tremendous overkill for the Clouds, and you’d be better off spending your money on new headphones.
A good general rule of thumb if you don’t like your current setup is to upgrade your headphones first. The quality of your headphones and their transducers are the most responsible for the sound hitting your ears, followed by the rest of your setup.
To put it another way, changing your headphones will make 90 percent of a difference, and changing your DAC will make the other 10 percent. So upgrading to something like the Nano, while probably audible depending on your current setup, won’t make a massive difference in overall quality or soundstage.
The two headphones you sold are generally regarded as sounding a bit wider than the Cloud Cores. If you’re looking for a true upgrade and you like a wide sound, I’d consider looking into Sennheiser’s open-backed 500 series lineup. Their entire design is centered around a wide soundstage and good audio quality.
The G Pro wouldn’t be that much better. It’s a little bit more natural in the treble, and it has a better microphone than the HyperX model. And a detachable cable. Their sound qualities are both in the same range of “Good,” just with a slightly different signature.