In reply to:
Would the stuff at 20 to 25 and below, be so loud with a 500 that I'd Have to turn the sub gain down enough that the sound at 30 to 35 would also be attenuated and take all the fun out of having the sub in the first place??!!
I'm hardly knowledgeable enough about this subject to be taken seriously but, it seems to me, that what you are concerned about would occur ONLY if there was a rise in the subs response at the lower frequencies (i.e, the 20 to 30 Hz material was louder than the the +30 Hz stuff. If you have a relatively flat response throughout the subs frequency range, achieved by placement, and/or room treatment, and/or equalization, the low stuff wouldn't be any louder than the higher stuff.
However, IF you found that low stuff to be "too much" for your comfort, and felt you had to lower the volume, then you might pay a price in overall subwoofer "oomph." So far, with my 500 (only one place for it, no room treatment, and unequalized), I haven't found that to be a problem.
I'm in a townhouse, that has one wall common with my neighbors (no children). I'm certain they can hear (feel) my 500 but, so far, have said nothing. I doubt the sub would be bothersome to them when listening to music, which I play at relatively low volumes. Movies, particularly action movies, are another kettle of fish. I try to follow basic rules of courtesy. I never watch movies past 11PM, and I only watch one or two a week, and not all of them are action flicks.
On the other hand, before the 500, I had a sub that started to roll off around 30 Hz. and it did a good job of rockin' my world. I don't think anyone who doesn't have a sub that reaches below 20Hz, should feel deprived. At the same time, there is something worthwhile added with a sub that does get down that low.
My satisfaction, and delight, with the 500 has more to do with the "smoothness" of it's performance than with it's low frequency response, though I'm certainly enjoying that as well. I haven't done any sweeps or measurements yet (waiting for the R-DES equalization system from Onix), but this doggone thing just seems to integrate with the rest of my system perfectly. "Smooth" is the word that keeps popping into my head. I'll be very interested to see just what my current frequency response is.