Should I use 2 speaker or 3 speakers?

[PCFan]

I recently bought a Sony HT-3360 HTiB system so I can get better quality sound than what my LCD TV produces. I don't plan on using all 5 speakers that came with it since this is in my bedroom and I have no place to set up the rear speakers. Is 3 speakers Dolby Digital and will 5.1 Dolby Digital downscale to 3 speaker if I only use 3 speakers or must I use all 5 speakers for Dolby Digital and 5.1 Dolby Digital? However, should I use the center speaker or will just 2 front speakers be enough for full dialogue sound?

Also I noticed that with my Xbox 360 connected to the receiver, if I don't use the center speaker, set the sound to Digital Stereo from the Dashboard, when I first press on the up arrow on my controller it's very quiet from the speakers but if I immediately press the up arrow again, the sound is at a normal volume unless I take like a 4 second rest in between a series of up arrow pressing in the Xbox dashboard. In 5.1 Stereo mode, which uses my center speaker, this volume problem doesn't happen. Is there something I have to do in my Receiver's setting to fix it if using 2 channel stereo in my Xbox 360?

[Canada]

you do not have to have 6 speakers to get a 5.1 mix (well yes you do), but having 3.0 you will get the most of the dialog out of center channel and other effects out of your left and right speakers.

Regarding the X Box 360 do you have an optical or HDMI cable for audio.