How do Subs and Receivers work together

Up until this past weekend, I had my B&W A600 sub plugged in directly into my Kuro 111FD via a sub output jack on the back of the set. Sounded great. I got great bass, from speech all the way to the big bangs.

On Saturday I purchased a 7.1 receiver along with two fronts and a center channel. I plugged the sub into the back on the receiver and now I have a few questions.

I know my sub is self powered, however I guess the volume I play the show I am watching affects the loudness of the sub. The sub now sounds...ugh... well not as clean as it did when hooked to the TV. I guess simply becuase the reciever can now push so much more power (volume) that the sub is not strong enough to keep up.

However the biggest question that I have is the speech coming from the speakers. There simply just isn't as much bass and depth in the speech when I am listening now compared to when hooked up to the TV. Having said this, I can clearly hear the sub when there is an explosion and so forth. So is there any significant relationship between a sub and a receiver and how it decodes speech?

Thanks.

I have a Pio VSX 52. I ran all of my calibration and so forth. I belive the issue is more so, now that I know a thing or two about frequencys, the frequency is speech is not low enough so that it will be pushed to the sub woofer via the reciever.

When my sub was hooked directly to the TV, the sub pushed everything out and in that set up, I don't think frequency level would ever have been a concerended.