Do you have the "wired remote control" plugged in? Did you buy this amp new or is this a refurb from us here at dB-r? If you "do" have the remote plugged in, unplug it and try again, you may have gotten the wrong remote control with your amp. If you look at the remote from the top, it is supposed to have a blue pot inside, if it is green, it is the wrong remote, and can cause symptoms like what you are talking about, if the amp came from dB-r, the green remote is "okay" because we mod the remote to work properly.
no i did not even try to hook up the remote.
If you don't have the remote plugged in, then it's possible your Sony amp had more power at 2 ohms. SAZ-1500D = 1 ohm amp. It is designed to run most efficiently and deliver full power output at 1 ohm. And if your sub is in a sealed box, your amp is likely never seeing close to 2 ohms period, probably 4 ohms at the lowest. Download WinISD, put in the parameters for your subwoofer and box and look at the "Impedance" plot, you will see what I mean....