First of all, iPod music will be stereo by default - for music listening, you will manually have to set the receiver to a mode like "Dolby ProLogic II" in order to simulate surround sound for a stereo source. A mode such as "All Channel Stereo" can sometimes be good for music, as it mostly preservers the stereo nature of the audio, but spreads it around equally to all speakers, whereas DPLII will only send small amounts of audio to the surround speakers.
For everything else, you mentioned in a previous post that your plan was to connect all devices (except the iPod, presumably) to the receiver via HDMI, then have single HDMI out from receiver to TV. Did you do this? That's how it SHOULD be set up - HDMI is capable of carrying digital surround audio information - provided the source has digital surround audio encoded with it.
If this is the case, the next step is to make sure each SOURCE device is configured to output digital surround audio and not simple stereo. I don't have an XBox or PS3, but I know they have various locations within their setup menus where you can specify the format of output audio.
Finally, once the sources are set up to output digital audio, and the connections between sources and receiver all support digital audio, is to make sure that the material you're watching is encoded with digital audio - as Robert alluded to, this is not always the case, particularly with TV broadcasts. If you get surround sound with some channels and not others the issue is likely the channel itself, and there's nothing you can do except use DPLII to simulate surround sound in those cases.
