I have comcast digital cable, and an HDTV cable box, which has an optical audio out connection, that i have going into my panasonic SC-HT900 receiver. The question is how come, some channels like HBO play on all the speakers, while others play only on the front 2. I know that these channels are not broadcast 5.1, but shouldn't they still play on all speakers in some kind of a non-true 5.1 fashion? Thanks for any info.
It all depends on what "mode" your receiver is in. Some movies on HBO are broadcast in Dolby Digital 5.1...so your receiver will likely pick that up immediately and change itself to "Dolby Digital" mode. If the broadcast is only in stereo (which most of them will be), it will be up to you to choose a sound mode. Try choosing Pro Logic II when you are on a "regular" channel (one not broadcasting in Dolby Digital), the sound should come out of all five speakers then.
My advice to you, is get rid of that piece of Junk, if you still have the receipt return it. I have the said animal in my bedroom and I hate it, I am getting an ONKYO 760, If you want to buy it let me know. Now on your question, because of the terrible engineering that panasonic does, Who knows?