What are you using to drive your speakers? I've had the same experience as you except with music. Had some people over and we were having a few "adult" beverages. After a while some wanted the music louder and then there's always someone that likes a particular song and when it starts they yell "turn it up"
My room isnt' real large and when I was at about -15 (on my Denon 3808, M60s and MVP100 fronts) people started to stop and stare, they couldn't believe it could be that loud and still sound that clear. When I bumped it up to -10 jaws dropped because even at the level every sound coming out was clearly defined and crystal clear. Like you I found that as you "put" the power to the speakers it gets better and better.
As an afterthought, I read somewhere, may have been on this forum that some people get a separate amp and use that to drive the large fronts, in my case M60s, and use the receiver to drive the center and surrounds. They say that since the amp is designed to do one thing, output music to speakers that it sounds much better than the music coming from the receiver. They say that because all the "specs" are better on the amp that even at low levels the sound it much more complete. I may have asked a "version" of this question on this forum but I don't really remember so if I have and someone responded to it please forgive me being redundant. Sometimes I post the same question on different forums and get completely different types of responses