How can you hook up a subwoofer up to a amp with only speaker level outputs? I have a 6 ohm subwoofer with only one way to hook it up, a RCA cable. The only outputs on my amp are speaker level. Is there a box out there you can buy online to hook up a sub with an RCA cable to speaker level outputs? I don't want to hurt anything my amp goes down to 4 ohms. thanks.