I've come to the conclusion that I will not get a 5.1 digital signal from the TV to the receiver. I don't think the TV will even pass the 5.1 signal on to the receiver - probably downmixing it to 2-channel stereo (there's only 2 speakers in the TV, after all) and then passing that along to receiver.
For blu-ray, make sure you select a format that is compatible with SPDIF (Dolby Digital, DTS) as it is doubtful that your TV can extract the core out of DTS HD:MA and DolbyTrueHD or pass 5.1 linear PCM.
Your cable box is probably using the same channel for HDMI or SPDIF.
I must admit, you lost me here...(alot of this is new to me)
Do you think that I may be correct that the cable box is incapable of making the correct recognition of where to send what signals?