Wire the switch to your power antenna lead off the radio going to the amp (remote turn on). The amp will turn off and on with the radio, and if the radio is on and you don't want the subs on for some reason, you can hit the switch. Don't wire the switch to the 12v supply from the battery, it would work fine, but if you forgot to turn the switch off, the amp would stay on while the car was off....not good. I don't really think you need one. I installed switches in some applications with factory head units. I didn't want to tap into the harness and find the antenna, so I just wired it to the cigarette lighter and threw a switch in. My Head Unit has a set of sub woofer outputs with subwoofer level. Just set it to 0. I still have power since the radio is on, but there's no signal, and thus no bass. I have a circuit breaker (intead of fuse)on the passenger floor board I can trip to cut power from the battery. Go with what you want to do. Good luck.
your amp does have a non-fading preout. which means that it will also likely have a NF control in the deck, which means you will be able to control the amp from the deck, and you dont need the separate switch. mt kenwood has a control to control sub amp level and to turn it off and on from the deck, its actually quite handy.