The number of channels and the number of speakers don't have to be the same. The receiver has various processing modes and the mode you use determines how the channels are mapped to the speakers.
Examples, rather than a lengthy explanation:
1. A normal 'redbook' music CD has two channels (left and right). Two channels is stereo.
- The receiver can send those 2 channels to two speakers if you put it in Stereo mode.
- The receiver can send those 2 channels to 5.1 speakers if you use a matrix decoder like Dolby ProLogic II or DTS:Neo6.
- The receiver can send those two channels to 6.1 speakers if you use a matrix mode like ProLogic IIx or DTS:Neo6. Pro Logic IIx can also turn 2 channel stereo into 7.1. [If you only have 5 speakers connected and indicated that in the receiver's setup, then PLIIx will not be available - only PLII]
2. A DVD-V (movie) has a Dolby Digital 5.1 track. There are 5.1 channels on the disc. The receiver will use the DD decoder to send each of the channels from the disc to each of the 5.1 speakers. If you had 7.1 speakers, you could use ProLogic IIx to play the 5.1 channels over 7.1 speakers. [There are currently no formats that contain 7.1 channels]
3. If you only have two speakers and tell the receiver that in the setup, when you play a disc with 5.1 channels, the receiver will downmix the 5.1 channels into 2 channels and play it over two speakers.
4. If you play a 5.1 source but tell the receiver you only have front left and right and 2 side surround speakers, but no center channel, the center channel will be folded into the left and right front channels.
There are dozens more possibilities. The key thing is that you tell the receiver which speakers are connected. Then you choose a processing mode (that is personal preference - I personally use PLII Music for pretty much everything - all sources, whether 2 channel or 5.1 play over all 5.1 speakers)
As far as making all the speakers play equally, that depends on what you mean. If you mean make all the channels sound equal in volume, that is done by calibrating the receiver with the internal test tones and that is another topic (search for it, you'll get lots of threads on the topic).
If you mean you want all the speakers to play regardless of the format of the source you are playing, then again it depends on which processing mode you choose. The receiver will automatically detect the format and choose the correct decoder for the common formats; eg if you play a DVD with a DD 5.1 track, it will automatically engage the DD decoder. You can of course change it to whatever you want at any time.
