If you prefer a flat curve, I'm not sure that either of the models you've mentioned will be ideal. The Kraken X is a v-shaped model, and the Xbox One Headset has some sculpting as well. The main reason for the Kraken X's extra "oomph" is its strong presence in the bass region, which the Xbox headset has less of due to its cloth pads that don't seal as well.
The Arctis 1 has a flatter sound in the same price range than either of those models, but I'm not sure if the Xbox store has any of those available in your region. I still like the Kraken X because it has an original design that doesn't skimp on features like some of Razer's previous budget models.
The Cloud II is still an excellent choice and as long as you're happy with its performance I'd just stick with using that honestly! You could always redeem those rewards points towards money to use on their digital games store.