The reason you need to adjust delay is to account for the time difference in processing the signal through the electronics in the 500 and in the SMS. With an analog sub without an equalizer no further delay is necessary since more time isn't required to process the signal. . Its only milliseconds but you should notice that the bass sounds more articulate and more seamless with your main speakers. The 2.5-3.0 ft delay is a good rule of thumb for digital processing in a device. In your case, I would experiment with setting delay around 14-15ft for the subwoofer. In effect the sub signal reaching the SMS and then the 500 is starting sooner than the signal to the main speakers. The "headstart" means the sounds should start at the same time at the speakers and sub. Otherwise the bass from the sub will lag and the overall combined bass will sound less distinct and "muddier".
