Well, my frustrations got the better of me lately, and I rectified my sub situation today.
As much as I'd love to add an EP500, or even an EP350, to my system, I just can't swing that much at the moment. But today I found a Klipsch SW-450 for a very reasonable price: about half the current price on Amazon.com.
The first testing session of 30 minutes or so indicates that this was a very good choice. Every BR scene has been distortion free, and the sofa is definitely vibrating, unlike the best the PDR-8 could do.
Tomorrow I'll re-run Audyssey and see how that goes. I'll play some DVD-A and SACD as well to see how musical this thing is. Other reviews indicate that this is the trade-off for this particular sub, but I'll see how it does in my small to medium room (about 1800 cubic feet).