After the shipment of these and my Denons went missing, I purchased another S400 and new AKG pads ($4 on ebay). The AKG pads that are being measured are stretched out due to being transplanted from a bigger driver housing. The consequence of a more loose fit I believe translates to poor controlled bass thats a little sloppy. The new AKG pads are a tighter fit and have little bit bass quality. After referencing The Paradox however, I went back to the stock pads and dampened cups to reduce the 'U' shaped response.
Marv, feel free to take these apart and change pads, etc if you want. I'm guessing you probably don't have much time these days to tinker though. Also, I'm in no hurry to get the shipment back if you want to hang on to them for a bit.