Are you getting sound from your surrounds in Dolby Digital or DTS? If yes, then check the input setup menu. On my receiver (Integra DTR 6.4), I can set it so that the default mode for an input is surround or two-channel. Also make sure the input, if digital, is selected as such. I don't know the Yamaha specifically, but if it has as many permutations in its set up as mine, it is easy to make the wrong setting by accident (the oversensitive joystick control on my remote makes this all too easy). However, even if you've set the input to two channel in your receiver, you should be able to override it with your remote, if it has a surround selector button.
Good luck, and I hope someone with a 1400 comes along to help.
To get multi-channel stereo simply press the stereo button on your remote numerous times. It will cycle between the various modes for stereo and multi-channel stereo operation.