While it's hard to find opinions online about one headphone vs another, because a lot of people seem to like to ignore the question and just give their own opinions that don't involve either, I did find this site that would let you kind of compare them side by side. The A40 seems to get a good boost from the Features category over the HyperX.
Personally, I would say go with the HyperX, I've had mine for over a year now and love it, although I have never tried the A40, so take that for what it's worth.