Infinity amps preamp limits

I am preparing to install a CarPC into my 2000 Montero Sport with the Infinity system. I hope there is someone that can tell me what pre amp voltage the stock amps can handle. My sub amp can handle 15V pre amp, but I'm sure the stock amps cannot come close. I plan to give the amps about 7V (or less), but I want to be sure they can hang so I don’t 'splode my stock system.