Which amp should I choose?

unless you want the kenwood KAC-9103D amplifier, don't get the kenwood. It will be running at 4 ohms so I would go with the MTX one. 533w RMS at 4 ohms is really good for these subwoofers. Keep the gain down just a tad, so no overheating occurs on the amplifier. But if you give the subwoofer less than 600w RMS you don't even have to worry about blowing a voice coil or suspension in the sub, because Rockford Fosgate tests over and over and underrates by about 50-100w on each subwoofer. Good luck man!