You gotta tell us more detail. Were you running omnis or cards? How thick was the bass? Check to see if you have your 9V pushin at least 7 volts? If you aren't juicing up those mics to the proper voltage, you are gonna get distortion and batteries on the way out are pretty much will give results like that. I have no experience with the denecke ps-2, so I do not know for sure that is the problem. But if you got a voltmeter, you should check the output from that box with those batteries you used at that show.
If you were running omnis then you should listen to my personal experience with 853s and omnis. I got a shitload of distortion one evening running a new set of 853 omni caps at a Supergrass show at the Showbox in Seattle...could never pin down the problem (and it wasn't pre distortion, I was using my trusty Sonosax > M1 combo). All I could say for sure was some sort of problem on the part of the 853 and the omni cap combo. I think the omnis got slammed real hard with amplified kick bass drums when I ran them up close (I was about 15-20 feet from the stage DFC). I am still pissed I didn't get that show cause Supergrass is such a blast to see. After that huge let down, I was not psyched to ever run the 853s again. Thus started my seemingly non-ending quest for a better and better stealth set up that would never let me down. And I am still searchin' b/c I am still noticing pros and cons of each high end stealth set up....