A DVD/TV question

I rent and play DVD movies thru my Sony TV. I have no home theater setup; I use only the speakers built into the TV. Problem is the dialog suffers in volume as if the DVD itself is set up for home theater use with a center channel. It's annoying because my wife and I have to crank up the volume to hear dialog that I'm presuming would be coming out of a center channel if I had one. Am I correct in my assumption that the rental DVDs are recorded this way? I experience no problem with normal TV broadcasts. Short of going to a home theater setup, is there an easy solution for my problem?