Depends on the choice of soundtrack (stereo vs. mch) and the particular player.
DVD and Blu-rays are normally mixed for more than two channel sound so you will be missing program material. An example would be surround sound mixes. Dialogue is mostly heard out of the centre channel speaker. It's surprising the amount of material that comes out of this channel!IMO this is the most critical speaker for home theatre applications.
Thanks for all the replies. I guess my question was vague. I was wondering if I used the stereo 2 channel analog ouput on my oppo player and add a center channel speaker fed from the same 2 channel analog stereo output would it be the same as if I used the 7.1 center channel output of the OPPO bdp-95 player to feed the center channel speaker? Put another way, do blu-ray dvds actually divide different parts of a movie sound track that require using 7.1 so everything can be heard?