Help with digital coaxial

I just bought a sony receiver that does "do" DTS and DOLBY DIGITAL and has both digital coaxial and fiber optic inputs. Since my DvD player only has digital coaxial output, I use that one. First I used the cable that came with the DvD, but when I connected the DvD to the receiver and played a DOLBY DIGITAL DvD movie it didnt display it as digital, instead it said PRO LOGIC, like if it was an analog signal. I tried messing around but couldnt change it. So I concluded that it was the cable that was very skinny, and cheap looking, maybe it was "ANALOG COAXIAL" or something. So I bought a MONSTER DIGITAL COAXIAL CABLE, FOR: DOLBY DIGITAL 5.1 SURROUND SOUND. And after using that cable I get the same problem. What could it be?
Also, I forgot to mention that the problem with having the PRO LOGIC instead of what I should have is that I dont have true surround. The back channels are only 1 channel. And they dont hear any different than from the front channels. So im not experiencing the full cinematic experience!
I'd appreciate the help allot.
Thanks.