If you still have your DVD player's remote you can simply learn it... the head to head way.
Plug your remote up to your computer via the cable. Open up your editor program and (1) Select DVD/Page One, (2) Select button to learn, (3) Click on the Learn button and with the two units head to head press the button on your DVD player remote that you want the button you selected on the MX-700 to learn (in this case it's the Play button), (4) Save the button (5) It will show learned and saved in this area after each step, (6) Save your file and then download it to your MX-700 after you are done learning and saving all your buttons.
Not sure it the codes for an F87 would work but
Remote Central has those codes for the MX-700 you could try. You might also make a post over there and ask if anyone happens to have that DVD player and the codes. They are usually pretty good about helping.
EDIT: Yep, I didn't even think about the idea in zorax2's post below... that could be easier.