If I remember correctly the Sony has a gain adjustment on it. If my memory is correct I would suspect you have the gain set too high for the sub and it just isn't able to handle the signal. Again, if I am correct about the Sony having a gain adjustment on it I believe this is the same pre-pro that a friend of mine kept blowing JBL speaker surrounds out with because the gain was set too high.
Subwoofer
Can anyone if possible answer why my subwoofer goes into stand by mode all the time after just a few minutes of playing if the song is base heavy its ok movies are better in paticular new films but i find myself always adjusting the gain up and down its a Sunfire True Subwoofer MK IV have mains center and rears set at 90 hz as the sub as well should i open the hz on the sub all the way but it gets to boomy i like tight tight bass at lowest db.I know this is a hard question to answer is it possible the sub itself is just getting old using old Sony ES 9000 for pre/pro. Thanx for the rookie question.😀.