Where do you have the subwoofer crossover set? Are you using the LFE crossover in your receiver or the crossover on the sub itself? You should use one or the other but not both.
The reason I ask is that a subwoofer is perfectly capable of putting out sound in the midrange. A subwoofer can move air, which is volume, at frequencies other than ones in the deep bass. You generally want to avoid this, if for nothing more than it makes voices guttural and muddy.
Check the audio settings on your new TV. Normally they should be off when using a A/V receiver. If not you may be getting sound from both your HDTV and A/V receiver.
My subwoofer is connected exactly as the old one was, via a single coax into the rear of my Onkyo 5009.
My TV's audio settings were set in the same manner as my old one, that being with its audio turned off because the A/V was doing it.
Again, the entire setup and the connections are the same as the previous ones with my just replaced TV.
BTW, I'm not complaining about this new "sound," because it sounds awesome. I'm just commenting that it would seem strange to have the sound more powerful and richer.