Generally if you want to max your subs potential, you want an amp with a higher wattage rating.
As most amps rate their wattage at 14.4v but our rsx will never run that continuously.
Our rsx's are generally around 13-13.5 so you will want to up the wattage rating to maybe a 700 rms if it even exists.
You wont use all that wattage anyways cause your front speakers wont be able to go as high as the sub. I would just get the cheaper kenwood and run with that power. Up to you but that alpine will work but for what? an extra 100 rms of power?