Someone help me with this av receiver question

[ren_of_heavenz]

I am looking to buy a 6.1 channel receiver.I have a few questions.
What if the source i connect with only outputs 5.1 audio?Will the 6th speaker be of any use in that case?What happens if i don't connect the 6th speaker to the 6.1 receiver and use only 5 speakers?
The 6.1 receiver i'm looking at has a digital optical out port but does not have hdmi out.I heard that optical can only carry 5 channel audio at most?Is that true?

 

[MDS]

- If you have 6.1 speakers connected but play a 5.1 source it will play over 5.1 speakers unless you use a matrix decoder like DD-EX or PLIIx to turn the 5.1 into 6.1.

- Digital connections (either optical or coax) use a protocol called S/PDIF (Sony/Philips Digital Interface Format). S/PDIF has bandwidth limitations but that is not necessarily related to channels. 5.1 formats like Dolby Digital/DTS and 6.1 formats like DD-EX and DTS-ES are compressed formats and do not exceed the maximum that can be carried over s/pdif. DTS 96/24 will also work over the digital connections because it too is compressed (if it were uncompressed it would exceed the bandwidth limitations). In other words, a digital connection will work for all current digital formats.

 

[ren_of_heavenz]

- If you have 6.1 speakers connected but play a 5.1 source it will play over 5.1 speakers unless you use a matrix decoder like DD-EX or PLIIx to turn the 5.1 into 6.1.

So if there is no matrix decoder in the 6.1 receiver and i don't hook up the 6th speaker to the receiver,it won't make any difference?

 

[HTHOLIC]

no difference

In that case there will be no difference regardless of whether you hook up the 6th speaker, in fact few sources are encoded in 6.1 and 7.1, what the codecs do is take the 5.1 signal and recopy some of the sound to the 6th or 7th speaker, sometimes it will edit the sound also.

DTS-ES is often used to do this for 6.1